subject:"\[PATCH 2\/3\] i2c\: bcm2835\: Add support for combined write\-read transfer"

Re: [PATCH 2/3] i2c: bcm2835: Add support for combined write-read transfer

2016-09-21 Thread Noralf Trønnes



Den 20.09.2016 13:29, skrev ker...@martin.sperl.org:

On 20.09.2016, at 12:56, Noralf Trønnes  wrote:


Den 20.09.2016 12:15, skrev Martin Sperl:


On 20.09.2016 10:41, Noralf Trønnes wrote:

Den 20.09.2016 09:19, skrev Martin Sperl:

Hi Noralf!

On 19.09.2016 17:26, Noralf Trønnes wrote:

Some SMBus protocols use Repeated Start Condition to switch from write
mode to read mode. Devices like MMA8451 won't work without it.

When downstream implemented support for this in i2c-bcm2708, it broke
support for some devices, so a module parameter was added and combined
transfer was disabled by default.
See https://github.com/raspberrypi/linux/issues/599
It doesn't seem to have been any investigation into what the problem
really was. Later there was added a timeout on the polling loop.

One of the devices mentioned to partially stop working was DS1307.

I have run thousands of transfers to a DS1307 (rtc), MMA8451 (accel)
and AT24C32 (eeprom) in parallel without problems.

Signed-off-by: Noralf Trønnes 
---
  drivers/i2c/busses/i2c-bcm2835.c | 107
+++
  1 file changed, 98 insertions(+), 9 deletions(-)

...

@@ -209,8 +289,17 @@ static int bcm2835_i2c_xfer(struct i2c_adapter
*adap, struct i2c_msg msgs[],
  int i;
  int ret = 0;
  +/* Combined write-read to the same address (smbus) */
+if (num == 2 && (msgs[0].addr == msgs[1].addr) &&
+!(msgs[0].flags & I2C_M_RD) && (msgs[1].flags & I2C_M_RD) &&
+(msgs[0].len <= 16)) {
+ret = bcm2835_i2c_xfer_msg(i2c_dev, [0], [1]);
+
+return ret ? ret : 2;
+}
+
  for (i = 0; i < num; i++) {
-ret = bcm2835_i2c_xfer_msg(i2c_dev, [i]);
+ret = bcm2835_i2c_xfer_msg(i2c_dev, [i], NULL);
  if (ret)
  break;
  }

This does not seem to implement the i2c_msg api correctly.

As per comments in include/uapi/linux/i2c.h on line 58 only the last
message
in a group should - by default - send a STOP.


Apparently it's a known problem that the i2c controller doesn't support
Repeated Start. It will always issue a Stop when it has transferred DLEN
bytes.
Refs:
http://www.circuitwizard.de/raspi-i2c-fix/raspi-i2c-fix.html
http://raspberrypi.stackexchange.com/questions/31728/has-anyone-successfully-used-i2c-repeated-starts-on-the-pi2-my-scope-says-they


UNLESS: a Start Transfer (ST) is issued after Transfer Active (TA) is set
and before DONE is set (or the last byte is shifted, I don't know excatly).
Refs:
https://github.com/raspberrypi/linux/issues/254#issuecomment-15254134
https://www.raspberrypi.org/forums/viewtopic.php?p=807834=2b612c7209f2175bf1a266359c72ae6c#p807834


I found this answer/report by joan that the downstream combined support
isn't reliable:
http://raspberrypi.stackexchange.com/questions/31728/has-anyone-successfully-used-i2c-repeated-starts-on-the-pi2-my-scope-says-they


My implementation differs from downstream in that I use local_irq_save()
to protect the polling loop. But that only protects from missing the TA
(downstream can miss the TA and issue a Stop).

So currently in mainline we have a driver that says it support the standard
(I2C_FUNC_I2C), but it really only supports one message transfers since it
can't do ReStart.

What I have done in this patch is to support ReStart for transfers with
2 messages: first write, then read. But maybe a better solution is to just
leave this alone if it is flaky and use bitbanging instead. I don't know.

I have not said that the approach you have taken is wrong or bad.


I didn't take it as such, I'm just not sure what's the best approach here,
so I added and looked up some more information


I was only telling you that the portion inside the bcm2835_i2c_xfer:
+/* Combined write-read to the same address (smbus) */
+if (num == 2 && (msgs[0].addr == msgs[1].addr) &&
+!(msgs[0].flags & I2C_M_RD) && (msgs[1].flags & I2C_M_RD) &&
+(msgs[0].len <= 16)) {
+ret = bcm2835_i2c_xfer_msg(i2c_dev, [0], [1]);
+
+return ret ? ret : 2;
+}
is very specific and maybe could be done in a "generic" manner
supporting more cases.


It has to be specific when it comes to number of messages. We can only
support ReStart after the first message unless we use polling for the
whole transfer. And in that case we can't disable interrupts for such
a long period and we will end up sometimes loosing Transfer Active,
resulting in Stop Condition between the messages.
So we can only do transfers with 2 messages if we want Restart.

It is possible to support more than 16 bytes for the first message,
filling the FIFO after polling TA, but I'm not sure that is common.
Mostly it's 1 or 2 bytes to set a register.
The write-read restriction isn't absolutely necessary either, but it's the
most common case I think. So it was about reusing bcm2835_i2c_xfer_msg().
A less restrictive approach would require a dedicated function I think.


At least add a dev_warn_once for all num >

Re: [PATCH 2/3] i2c: bcm2835: Add support for combined write-read transfer

2016-09-21 Thread Noralf Trønnes



Den 20.09.2016 13:29, skrev ker...@martin.sperl.org:

On 20.09.2016, at 12:56, Noralf Trønnes  wrote:


Den 20.09.2016 12:15, skrev Martin Sperl:


On 20.09.2016 10:41, Noralf Trønnes wrote:

Den 20.09.2016 09:19, skrev Martin Sperl:

Hi Noralf!

On 19.09.2016 17:26, Noralf Trønnes wrote:

Some SMBus protocols use Repeated Start Condition to switch from write
mode to read mode. Devices like MMA8451 won't work without it.

When downstream implemented support for this in i2c-bcm2708, it broke
support for some devices, so a module parameter was added and combined
transfer was disabled by default.
See https://github.com/raspberrypi/linux/issues/599
It doesn't seem to have been any investigation into what the problem
really was. Later there was added a timeout on the polling loop.

One of the devices mentioned to partially stop working was DS1307.

I have run thousands of transfers to a DS1307 (rtc), MMA8451 (accel)
and AT24C32 (eeprom) in parallel without problems.

Signed-off-by: Noralf Trønnes 
---
  drivers/i2c/busses/i2c-bcm2835.c | 107
+++
  1 file changed, 98 insertions(+), 9 deletions(-)

...

@@ -209,8 +289,17 @@ static int bcm2835_i2c_xfer(struct i2c_adapter
*adap, struct i2c_msg msgs[],
  int i;
  int ret = 0;
  +/* Combined write-read to the same address (smbus) */
+if (num == 2 && (msgs[0].addr == msgs[1].addr) &&
+!(msgs[0].flags & I2C_M_RD) && (msgs[1].flags & I2C_M_RD) &&
+(msgs[0].len <= 16)) {
+ret = bcm2835_i2c_xfer_msg(i2c_dev, [0], [1]);
+
+return ret ? ret : 2;
+}
+
  for (i = 0; i < num; i++) {
-ret = bcm2835_i2c_xfer_msg(i2c_dev, [i]);
+ret = bcm2835_i2c_xfer_msg(i2c_dev, [i], NULL);
  if (ret)
  break;
  }

This does not seem to implement the i2c_msg api correctly.

As per comments in include/uapi/linux/i2c.h on line 58 only the last
message
in a group should - by default - send a STOP.


Apparently it's a known problem that the i2c controller doesn't support
Repeated Start. It will always issue a Stop when it has transferred DLEN
bytes.
Refs:
http://www.circuitwizard.de/raspi-i2c-fix/raspi-i2c-fix.html
http://raspberrypi.stackexchange.com/questions/31728/has-anyone-successfully-used-i2c-repeated-starts-on-the-pi2-my-scope-says-they


UNLESS: a Start Transfer (ST) is issued after Transfer Active (TA) is set
and before DONE is set (or the last byte is shifted, I don't know excatly).
Refs:
https://github.com/raspberrypi/linux/issues/254#issuecomment-15254134
https://www.raspberrypi.org/forums/viewtopic.php?p=807834=2b612c7209f2175bf1a266359c72ae6c#p807834


I found this answer/report by joan that the downstream combined support
isn't reliable:
http://raspberrypi.stackexchange.com/questions/31728/has-anyone-successfully-used-i2c-repeated-starts-on-the-pi2-my-scope-says-they


My implementation differs from downstream in that I use local_irq_save()
to protect the polling loop. But that only protects from missing the TA
(downstream can miss the TA and issue a Stop).

So currently in mainline we have a driver that says it support the standard
(I2C_FUNC_I2C), but it really only supports one message transfers since it
can't do ReStart.

What I have done in this patch is to support ReStart for transfers with
2 messages: first write, then read. But maybe a better solution is to just
leave this alone if it is flaky and use bitbanging instead. I don't know.

I have not said that the approach you have taken is wrong or bad.


I didn't take it as such, I'm just not sure what's the best approach here,
so I added and looked up some more information


I was only telling you that the portion inside the bcm2835_i2c_xfer:
+/* Combined write-read to the same address (smbus) */
+if (num == 2 && (msgs[0].addr == msgs[1].addr) &&
+!(msgs[0].flags & I2C_M_RD) && (msgs[1].flags & I2C_M_RD) &&
+(msgs[0].len <= 16)) {
+ret = bcm2835_i2c_xfer_msg(i2c_dev, [0], [1]);
+
+return ret ? ret : 2;
+}
is very specific and maybe could be done in a "generic" manner
supporting more cases.


It has to be specific when it comes to number of messages. We can only
support ReStart after the first message unless we use polling for the
whole transfer. And in that case we can't disable interrupts for such
a long period and we will end up sometimes loosing Transfer Active,
resulting in Stop Condition between the messages.
So we can only do transfers with 2 messages if we want Restart.

It is possible to support more than 16 bytes for the first message,
filling the FIFO after polling TA, but I'm not sure that is common.
Mostly it's 1 or 2 bytes to set a register.
The write-read restriction isn't absolutely necessary either, but it's the
most common case I think. So it was about reusing bcm2835_i2c_xfer_msg().
A less restrictive approach would require a dedicated function I think.


At least add a dev_warn_once for all num > 1 cases not handled by the
code above.

Re: [PATCH 2/3] i2c: bcm2835: Add support for combined write-read transfer

2016-09-20 Thread kernel


> On 20.09.2016, at 12:56, Noralf Trønnes  wrote:
> 
> 
> Den 20.09.2016 12:15, skrev Martin Sperl:
>> 
>> 
>> On 20.09.2016 10:41, Noralf Trønnes wrote:
>>> 
>>> Den 20.09.2016 09:19, skrev Martin Sperl:
 Hi Noralf!
 
 On 19.09.2016 17:26, Noralf Trønnes wrote:
> Some SMBus protocols use Repeated Start Condition to switch from write
> mode to read mode. Devices like MMA8451 won't work without it.
> 
> When downstream implemented support for this in i2c-bcm2708, it broke
> support for some devices, so a module parameter was added and combined
> transfer was disabled by default.
> See https://github.com/raspberrypi/linux/issues/599
> It doesn't seem to have been any investigation into what the problem
> really was. Later there was added a timeout on the polling loop.
> 
> One of the devices mentioned to partially stop working was DS1307.
> 
> I have run thousands of transfers to a DS1307 (rtc), MMA8451 (accel)
> and AT24C32 (eeprom) in parallel without problems.
> 
> Signed-off-by: Noralf Trønnes 
> ---
>  drivers/i2c/busses/i2c-bcm2835.c | 107
> +++
>  1 file changed, 98 insertions(+), 9 deletions(-)
 ...
> @@ -209,8 +289,17 @@ static int bcm2835_i2c_xfer(struct i2c_adapter
> *adap, struct i2c_msg msgs[],
>  int i;
>  int ret = 0;
>  +/* Combined write-read to the same address (smbus) */
> +if (num == 2 && (msgs[0].addr == msgs[1].addr) &&
> +!(msgs[0].flags & I2C_M_RD) && (msgs[1].flags & I2C_M_RD) &&
> +(msgs[0].len <= 16)) {
> +ret = bcm2835_i2c_xfer_msg(i2c_dev, [0], [1]);
> +
> +return ret ? ret : 2;
> +}
> +
>  for (i = 0; i < num; i++) {
> -ret = bcm2835_i2c_xfer_msg(i2c_dev, [i]);
> +ret = bcm2835_i2c_xfer_msg(i2c_dev, [i], NULL);
>  if (ret)
>  break;
>  }
 This does not seem to implement the i2c_msg api correctly.
 
 As per comments in include/uapi/linux/i2c.h on line 58 only the last
 message
 in a group should - by default - send a STOP.
 
>>> 
>>> Apparently it's a known problem that the i2c controller doesn't support
>>> Repeated Start. It will always issue a Stop when it has transferred DLEN
>>> bytes.
>>> Refs:
>>> http://www.circuitwizard.de/raspi-i2c-fix/raspi-i2c-fix.html
>>> http://raspberrypi.stackexchange.com/questions/31728/has-anyone-successfully-used-i2c-repeated-starts-on-the-pi2-my-scope-says-they
>>>  
>>> 
>>> 
>>> UNLESS: a Start Transfer (ST) is issued after Transfer Active (TA) is set
>>> and before DONE is set (or the last byte is shifted, I don't know excatly).
>>> Refs:
>>> https://github.com/raspberrypi/linux/issues/254#issuecomment-15254134
>>> https://www.raspberrypi.org/forums/viewtopic.php?p=807834=2b612c7209f2175bf1a266359c72ae6c#p807834
>>>  
>>> 
>>> 
>>> I found this answer/report by joan that the downstream combined support
>>> isn't reliable:
>>> http://raspberrypi.stackexchange.com/questions/31728/has-anyone-successfully-used-i2c-repeated-starts-on-the-pi2-my-scope-says-they
>>>  
>>> 
>>> 
>>> My implementation differs from downstream in that I use local_irq_save()
>>> to protect the polling loop. But that only protects from missing the TA
>>> (downstream can miss the TA and issue a Stop).
>>> 
>>> So currently in mainline we have a driver that says it support the standard
>>> (I2C_FUNC_I2C), but it really only supports one message transfers since it
>>> can't do ReStart.
>>> 
>>> What I have done in this patch is to support ReStart for transfers with
>>> 2 messages: first write, then read. But maybe a better solution is to just
>>> leave this alone if it is flaky and use bitbanging instead. I don't know.
>> I have not said that the approach you have taken is wrong or bad.
>> 
> 
> I didn't take it as such, I'm just not sure what's the best approach here,
> so I added and looked up some more information
> 
>> I was only telling you that the portion inside the bcm2835_i2c_xfer:
>> +/* Combined write-read to the same address (smbus) */
>> +if (num == 2 && (msgs[0].addr == msgs[1].addr) &&
>> +!(msgs[0].flags & I2C_M_RD) && (msgs[1].flags & I2C_M_RD) &&
>> +(msgs[0].len <= 16)) {
>> +ret = bcm2835_i2c_xfer_msg(i2c_dev, [0], [1]);
>> +
>> +return ret ? ret : 2;
>> +}
>> is very specific and maybe could be done in a "generic" manner
>> supporting more cases.
>> 
> 
> It has to be specific when it comes to number of messages. We can only
> support ReStart after the first message unless we use polling for the
> whole transfer. And in that case we can't disable interrupts for such
> a long period and we will end up sometimes loosing Transfer Active,
> resulting in Stop Condition between the messages.
> So we can only do transfers with 2 messages if we want Restart.

Re: [PATCH 2/3] i2c: bcm2835: Add support for combined write-read transfer

2016-09-20 Thread kernel


> On 20.09.2016, at 12:56, Noralf Trønnes  wrote:
> 
> 
> Den 20.09.2016 12:15, skrev Martin Sperl:
>> 
>> 
>> On 20.09.2016 10:41, Noralf Trønnes wrote:
>>> 
>>> Den 20.09.2016 09:19, skrev Martin Sperl:
 Hi Noralf!
 
 On 19.09.2016 17:26, Noralf Trønnes wrote:
> Some SMBus protocols use Repeated Start Condition to switch from write
> mode to read mode. Devices like MMA8451 won't work without it.
> 
> When downstream implemented support for this in i2c-bcm2708, it broke
> support for some devices, so a module parameter was added and combined
> transfer was disabled by default.
> See https://github.com/raspberrypi/linux/issues/599
> It doesn't seem to have been any investigation into what the problem
> really was. Later there was added a timeout on the polling loop.
> 
> One of the devices mentioned to partially stop working was DS1307.
> 
> I have run thousands of transfers to a DS1307 (rtc), MMA8451 (accel)
> and AT24C32 (eeprom) in parallel without problems.
> 
> Signed-off-by: Noralf Trønnes 
> ---
>  drivers/i2c/busses/i2c-bcm2835.c | 107
> +++
>  1 file changed, 98 insertions(+), 9 deletions(-)
 ...
> @@ -209,8 +289,17 @@ static int bcm2835_i2c_xfer(struct i2c_adapter
> *adap, struct i2c_msg msgs[],
>  int i;
>  int ret = 0;
>  +/* Combined write-read to the same address (smbus) */
> +if (num == 2 && (msgs[0].addr == msgs[1].addr) &&
> +!(msgs[0].flags & I2C_M_RD) && (msgs[1].flags & I2C_M_RD) &&
> +(msgs[0].len <= 16)) {
> +ret = bcm2835_i2c_xfer_msg(i2c_dev, [0], [1]);
> +
> +return ret ? ret : 2;
> +}
> +
>  for (i = 0; i < num; i++) {
> -ret = bcm2835_i2c_xfer_msg(i2c_dev, [i]);
> +ret = bcm2835_i2c_xfer_msg(i2c_dev, [i], NULL);
>  if (ret)
>  break;
>  }
 This does not seem to implement the i2c_msg api correctly.
 
 As per comments in include/uapi/linux/i2c.h on line 58 only the last
 message
 in a group should - by default - send a STOP.
 
>>> 
>>> Apparently it's a known problem that the i2c controller doesn't support
>>> Repeated Start. It will always issue a Stop when it has transferred DLEN
>>> bytes.
>>> Refs:
>>> http://www.circuitwizard.de/raspi-i2c-fix/raspi-i2c-fix.html
>>> http://raspberrypi.stackexchange.com/questions/31728/has-anyone-successfully-used-i2c-repeated-starts-on-the-pi2-my-scope-says-they
>>>  
>>> 
>>> 
>>> UNLESS: a Start Transfer (ST) is issued after Transfer Active (TA) is set
>>> and before DONE is set (or the last byte is shifted, I don't know excatly).
>>> Refs:
>>> https://github.com/raspberrypi/linux/issues/254#issuecomment-15254134
>>> https://www.raspberrypi.org/forums/viewtopic.php?p=807834=2b612c7209f2175bf1a266359c72ae6c#p807834
>>>  
>>> 
>>> 
>>> I found this answer/report by joan that the downstream combined support
>>> isn't reliable:
>>> http://raspberrypi.stackexchange.com/questions/31728/has-anyone-successfully-used-i2c-repeated-starts-on-the-pi2-my-scope-says-they
>>>  
>>> 
>>> 
>>> My implementation differs from downstream in that I use local_irq_save()
>>> to protect the polling loop. But that only protects from missing the TA
>>> (downstream can miss the TA and issue a Stop).
>>> 
>>> So currently in mainline we have a driver that says it support the standard
>>> (I2C_FUNC_I2C), but it really only supports one message transfers since it
>>> can't do ReStart.
>>> 
>>> What I have done in this patch is to support ReStart for transfers with
>>> 2 messages: first write, then read. But maybe a better solution is to just
>>> leave this alone if it is flaky and use bitbanging instead. I don't know.
>> I have not said that the approach you have taken is wrong or bad.
>> 
> 
> I didn't take it as such, I'm just not sure what's the best approach here,
> so I added and looked up some more information
> 
>> I was only telling you that the portion inside the bcm2835_i2c_xfer:
>> +/* Combined write-read to the same address (smbus) */
>> +if (num == 2 && (msgs[0].addr == msgs[1].addr) &&
>> +!(msgs[0].flags & I2C_M_RD) && (msgs[1].flags & I2C_M_RD) &&
>> +(msgs[0].len <= 16)) {
>> +ret = bcm2835_i2c_xfer_msg(i2c_dev, [0], [1]);
>> +
>> +return ret ? ret : 2;
>> +}
>> is very specific and maybe could be done in a "generic" manner
>> supporting more cases.
>> 
> 
> It has to be specific when it comes to number of messages. We can only
> support ReStart after the first message unless we use polling for the
> whole transfer. And in that case we can't disable interrupts for such
> a long period and we will end up sometimes loosing Transfer Active,
> resulting in Stop Condition between the messages.
> So we can only do transfers with 2 messages if we want Restart.
> 
> It is possible to support more

Re: [PATCH 2/3] i2c: bcm2835: Add support for combined write-read transfer

2016-09-20 Thread Noralf Trønnes



Den 20.09.2016 12:15, skrev Martin Sperl:



On 20.09.2016 10:41, Noralf Trønnes wrote:


Den 20.09.2016 09:19, skrev Martin Sperl:

Hi Noralf!

On 19.09.2016 17:26, Noralf Trønnes wrote:

Some SMBus protocols use Repeated Start Condition to switch from write
mode to read mode. Devices like MMA8451 won't work without it.

When downstream implemented support for this in i2c-bcm2708, it broke
support for some devices, so a module parameter was added and combined
transfer was disabled by default.
See https://github.com/raspberrypi/linux/issues/599
It doesn't seem to have been any investigation into what the problem
really was. Later there was added a timeout on the polling loop.

One of the devices mentioned to partially stop working was DS1307.

I have run thousands of transfers to a DS1307 (rtc), MMA8451 (accel)
and AT24C32 (eeprom) in parallel without problems.

Signed-off-by: Noralf Trønnes 
---
  drivers/i2c/busses/i2c-bcm2835.c | 107
+++
  1 file changed, 98 insertions(+), 9 deletions(-)

...

@@ -209,8 +289,17 @@ static int bcm2835_i2c_xfer(struct i2c_adapter
*adap, struct i2c_msg msgs[],
  int i;
  int ret = 0;
  +/* Combined write-read to the same address (smbus) */
+if (num == 2 && (msgs[0].addr == msgs[1].addr) &&
+!(msgs[0].flags & I2C_M_RD) && (msgs[1].flags & I2C_M_RD) &&
+(msgs[0].len <= 16)) {
+ret = bcm2835_i2c_xfer_msg(i2c_dev, [0], [1]);
+
+return ret ? ret : 2;
+}
+
  for (i = 0; i < num; i++) {
-ret = bcm2835_i2c_xfer_msg(i2c_dev, [i]);
+ret = bcm2835_i2c_xfer_msg(i2c_dev, [i], NULL);
  if (ret)
  break;
  }

This does not seem to implement the i2c_msg api correctly.

As per comments in include/uapi/linux/i2c.h on line 58 only the last
message
in a group should - by default - send a STOP.



Apparently it's a known problem that the i2c controller doesn't support
Repeated Start. It will always issue a Stop when it has transferred DLEN
bytes.
Refs:
http://www.circuitwizard.de/raspi-i2c-fix/raspi-i2c-fix.html
http://raspberrypi.stackexchange.com/questions/31728/has-anyone-successfully-used-i2c-repeated-starts-on-the-pi2-my-scope-says-they 




UNLESS: a Start Transfer (ST) is issued after Transfer Active (TA) is 
set
and before DONE is set (or the last byte is shifted, I don't know 
excatly).

Refs:
https://github.com/raspberrypi/linux/issues/254#issuecomment-15254134
https://www.raspberrypi.org/forums/viewtopic.php?p=807834=2b612c7209f2175bf1a266359c72ae6c#p807834 




I found this answer/report by joan that the downstream combined support
isn't reliable:
http://raspberrypi.stackexchange.com/questions/31728/has-anyone-successfully-used-i2c-repeated-starts-on-the-pi2-my-scope-says-they 




My implementation differs from downstream in that I use local_irq_save()
to protect the polling loop. But that only protects from missing the TA
(downstream can miss the TA and issue a Stop).

So currently in mainline we have a driver that says it support the 
standard
(I2C_FUNC_I2C), but it really only supports one message transfers 
since it

can't do ReStart.

What I have done in this patch is to support ReStart for transfers with
2 messages: first write, then read. But maybe a better solution is to 
just
leave this alone if it is flaky and use bitbanging instead. I don't 
know.

I have not said that the approach you have taken is wrong or bad.



I didn't take it as such, I'm just not sure what's the best approach here,
so I added and looked up some more information


I was only telling you that the portion inside the bcm2835_i2c_xfer:
+/* Combined write-read to the same address (smbus) */
+if (num == 2 && (msgs[0].addr == msgs[1].addr) &&
+!(msgs[0].flags & I2C_M_RD) && (msgs[1].flags & I2C_M_RD) &&
+(msgs[0].len <= 16)) {
+ret = bcm2835_i2c_xfer_msg(i2c_dev, [0], [1]);
+
+return ret ? ret : 2;
+}
is very specific and maybe could be done in a "generic" manner
supporting more cases.



It has to be specific when it comes to number of messages. We can only
support ReStart after the first message unless we use polling for the
whole transfer. And in that case we can't disable interrupts for such
a long period and we will end up sometimes loosing Transfer Active,
resulting in Stop Condition between the messages.
So we can only do transfers with 2 messages if we want Restart.

It is possible to support more than 16 bytes for the first message,
filling the FIFO after polling TA, but I'm not sure that is common.
Mostly it's 1 or 2 bytes to set a register.
The write-read restriction isn't absolutely necessary either, but it's the
most common case I think. So it was about reusing bcm2835_i2c_xfer_msg().
A less restrictive approach would require a dedicated function I think.


At least add a dev_warn_once for all num > 1 cases not handled by the
code above.

This gives people an opportunity to detect such a situation if

Re: [PATCH 2/3] i2c: bcm2835: Add support for combined write-read transfer

2016-09-20 Thread Noralf Trønnes



Den 20.09.2016 12:15, skrev Martin Sperl:



On 20.09.2016 10:41, Noralf Trønnes wrote:


Den 20.09.2016 09:19, skrev Martin Sperl:

Hi Noralf!

On 19.09.2016 17:26, Noralf Trønnes wrote:

Some SMBus protocols use Repeated Start Condition to switch from write
mode to read mode. Devices like MMA8451 won't work without it.

When downstream implemented support for this in i2c-bcm2708, it broke
support for some devices, so a module parameter was added and combined
transfer was disabled by default.
See https://github.com/raspberrypi/linux/issues/599
It doesn't seem to have been any investigation into what the problem
really was. Later there was added a timeout on the polling loop.

One of the devices mentioned to partially stop working was DS1307.

I have run thousands of transfers to a DS1307 (rtc), MMA8451 (accel)
and AT24C32 (eeprom) in parallel without problems.

Signed-off-by: Noralf Trønnes 
---
  drivers/i2c/busses/i2c-bcm2835.c | 107
+++
  1 file changed, 98 insertions(+), 9 deletions(-)

...

@@ -209,8 +289,17 @@ static int bcm2835_i2c_xfer(struct i2c_adapter
*adap, struct i2c_msg msgs[],
  int i;
  int ret = 0;
  +/* Combined write-read to the same address (smbus) */
+if (num == 2 && (msgs[0].addr == msgs[1].addr) &&
+!(msgs[0].flags & I2C_M_RD) && (msgs[1].flags & I2C_M_RD) &&
+(msgs[0].len <= 16)) {
+ret = bcm2835_i2c_xfer_msg(i2c_dev, [0], [1]);
+
+return ret ? ret : 2;
+}
+
  for (i = 0; i < num; i++) {
-ret = bcm2835_i2c_xfer_msg(i2c_dev, [i]);
+ret = bcm2835_i2c_xfer_msg(i2c_dev, [i], NULL);
  if (ret)
  break;
  }

This does not seem to implement the i2c_msg api correctly.

As per comments in include/uapi/linux/i2c.h on line 58 only the last
message
in a group should - by default - send a STOP.



Apparently it's a known problem that the i2c controller doesn't support
Repeated Start. It will always issue a Stop when it has transferred DLEN
bytes.
Refs:
http://www.circuitwizard.de/raspi-i2c-fix/raspi-i2c-fix.html
http://raspberrypi.stackexchange.com/questions/31728/has-anyone-successfully-used-i2c-repeated-starts-on-the-pi2-my-scope-says-they 




UNLESS: a Start Transfer (ST) is issued after Transfer Active (TA) is 
set
and before DONE is set (or the last byte is shifted, I don't know 
excatly).

Refs:
https://github.com/raspberrypi/linux/issues/254#issuecomment-15254134
https://www.raspberrypi.org/forums/viewtopic.php?p=807834=2b612c7209f2175bf1a266359c72ae6c#p807834 




I found this answer/report by joan that the downstream combined support
isn't reliable:
http://raspberrypi.stackexchange.com/questions/31728/has-anyone-successfully-used-i2c-repeated-starts-on-the-pi2-my-scope-says-they 




My implementation differs from downstream in that I use local_irq_save()
to protect the polling loop. But that only protects from missing the TA
(downstream can miss the TA and issue a Stop).

So currently in mainline we have a driver that says it support the 
standard
(I2C_FUNC_I2C), but it really only supports one message transfers 
since it

can't do ReStart.

What I have done in this patch is to support ReStart for transfers with
2 messages: first write, then read. But maybe a better solution is to 
just
leave this alone if it is flaky and use bitbanging instead. I don't 
know.

I have not said that the approach you have taken is wrong or bad.



I didn't take it as such, I'm just not sure what's the best approach here,
so I added and looked up some more information


I was only telling you that the portion inside the bcm2835_i2c_xfer:
+/* Combined write-read to the same address (smbus) */
+if (num == 2 && (msgs[0].addr == msgs[1].addr) &&
+!(msgs[0].flags & I2C_M_RD) && (msgs[1].flags & I2C_M_RD) &&
+(msgs[0].len <= 16)) {
+ret = bcm2835_i2c_xfer_msg(i2c_dev, [0], [1]);
+
+return ret ? ret : 2;
+}
is very specific and maybe could be done in a "generic" manner
supporting more cases.



It has to be specific when it comes to number of messages. We can only
support ReStart after the first message unless we use polling for the
whole transfer. And in that case we can't disable interrupts for such
a long period and we will end up sometimes loosing Transfer Active,
resulting in Stop Condition between the messages.
So we can only do transfers with 2 messages if we want Restart.

It is possible to support more than 16 bytes for the first message,
filling the FIFO after polling TA, but I'm not sure that is common.
Mostly it's 1 or 2 bytes to set a register.
The write-read restriction isn't absolutely necessary either, but it's the
most common case I think. So it was about reusing bcm2835_i2c_xfer_msg().
A less restrictive approach would require a dedicated function I think.


At least add a dev_warn_once for all num > 1 cases not handled by the
code above.

This gives people an opportunity to detect such a situation if they
find something

Re: [PATCH 2/3] i2c: bcm2835: Add support for combined write-read transfer

2016-09-20 Thread Martin Sperl




On 20.09.2016 10:41, Noralf Trønnes wrote:


Den 20.09.2016 09:19, skrev Martin Sperl:

Hi Noralf!

On 19.09.2016 17:26, Noralf Trønnes wrote:

Some SMBus protocols use Repeated Start Condition to switch from write
mode to read mode. Devices like MMA8451 won't work without it.

When downstream implemented support for this in i2c-bcm2708, it broke
support for some devices, so a module parameter was added and combined
transfer was disabled by default.
See https://github.com/raspberrypi/linux/issues/599
It doesn't seem to have been any investigation into what the problem
really was. Later there was added a timeout on the polling loop.

One of the devices mentioned to partially stop working was DS1307.

I have run thousands of transfers to a DS1307 (rtc), MMA8451 (accel)
and AT24C32 (eeprom) in parallel without problems.

Signed-off-by: Noralf Trønnes 
---
  drivers/i2c/busses/i2c-bcm2835.c | 107
+++
  1 file changed, 98 insertions(+), 9 deletions(-)

...

@@ -209,8 +289,17 @@ static int bcm2835_i2c_xfer(struct i2c_adapter
*adap, struct i2c_msg msgs[],
  int i;
  int ret = 0;
  +/* Combined write-read to the same address (smbus) */
+if (num == 2 && (msgs[0].addr == msgs[1].addr) &&
+!(msgs[0].flags & I2C_M_RD) && (msgs[1].flags & I2C_M_RD) &&
+(msgs[0].len <= 16)) {
+ret = bcm2835_i2c_xfer_msg(i2c_dev, [0], [1]);
+
+return ret ? ret : 2;
+}
+
  for (i = 0; i < num; i++) {
-ret = bcm2835_i2c_xfer_msg(i2c_dev, [i]);
+ret = bcm2835_i2c_xfer_msg(i2c_dev, [i], NULL);
  if (ret)
  break;
  }

This does not seem to implement the i2c_msg api correctly.

As per comments in include/uapi/linux/i2c.h on line 58 only the last
message
in a group should - by default - send a STOP.



Apparently it's a known problem that the i2c controller doesn't support
Repeated Start. It will always issue a Stop when it has transferred DLEN
bytes.
Refs:
http://www.circuitwizard.de/raspi-i2c-fix/raspi-i2c-fix.html
http://raspberrypi.stackexchange.com/questions/31728/has-anyone-successfully-used-i2c-repeated-starts-on-the-pi2-my-scope-says-they


UNLESS: a Start Transfer (ST) is issued after Transfer Active (TA) is set
and before DONE is set (or the last byte is shifted, I don't know excatly).
Refs:
https://github.com/raspberrypi/linux/issues/254#issuecomment-15254134
https://www.raspberrypi.org/forums/viewtopic.php?p=807834=2b612c7209f2175bf1a266359c72ae6c#p807834


I found this answer/report by joan that the downstream combined support
isn't reliable:
http://raspberrypi.stackexchange.com/questions/31728/has-anyone-successfully-used-i2c-repeated-starts-on-the-pi2-my-scope-says-they


My implementation differs from downstream in that I use local_irq_save()
to protect the polling loop. But that only protects from missing the TA
(downstream can miss the TA and issue a Stop).

So currently in mainline we have a driver that says it support the standard
(I2C_FUNC_I2C), but it really only supports one message transfers since it
can't do ReStart.

What I have done in this patch is to support ReStart for transfers with
2 messages: first write, then read. But maybe a better solution is to just
leave this alone if it is flaky and use bitbanging instead. I don't know.

I have not said that the approach you have taken is wrong or bad.

I was only telling you that the portion inside the bcm2835_i2c_xfer:
+   /* Combined write-read to the same address (smbus) */
+   if (num == 2 && (msgs[0].addr == msgs[1].addr) &&
+   !(msgs[0].flags & I2C_M_RD) && (msgs[1].flags & I2C_M_RD) &&
+   (msgs[0].len <= 16)) {
+   ret = bcm2835_i2c_xfer_msg(i2c_dev, [0], [1]);
+
+   return ret ? ret : 2;
+   }
is very specific and maybe could be done in a "generic" manner
supporting more cases.

At least add a dev_warn_once for all num > 1 cases not handled by the
code above.

This gives people an opportunity to detect such a situation if they
find something is not working as expected.

Martin

Re: [PATCH 2/3] i2c: bcm2835: Add support for combined write-read transfer

2016-09-20 Thread Martin Sperl




On 20.09.2016 10:41, Noralf Trønnes wrote:


Den 20.09.2016 09:19, skrev Martin Sperl:

Hi Noralf!

On 19.09.2016 17:26, Noralf Trønnes wrote:

Some SMBus protocols use Repeated Start Condition to switch from write
mode to read mode. Devices like MMA8451 won't work without it.

When downstream implemented support for this in i2c-bcm2708, it broke
support for some devices, so a module parameter was added and combined
transfer was disabled by default.
See https://github.com/raspberrypi/linux/issues/599
It doesn't seem to have been any investigation into what the problem
really was. Later there was added a timeout on the polling loop.

One of the devices mentioned to partially stop working was DS1307.

I have run thousands of transfers to a DS1307 (rtc), MMA8451 (accel)
and AT24C32 (eeprom) in parallel without problems.

Signed-off-by: Noralf Trønnes 
---
  drivers/i2c/busses/i2c-bcm2835.c | 107
+++
  1 file changed, 98 insertions(+), 9 deletions(-)

...

@@ -209,8 +289,17 @@ static int bcm2835_i2c_xfer(struct i2c_adapter
*adap, struct i2c_msg msgs[],
  int i;
  int ret = 0;
  +/* Combined write-read to the same address (smbus) */
+if (num == 2 && (msgs[0].addr == msgs[1].addr) &&
+!(msgs[0].flags & I2C_M_RD) && (msgs[1].flags & I2C_M_RD) &&
+(msgs[0].len <= 16)) {
+ret = bcm2835_i2c_xfer_msg(i2c_dev, [0], [1]);
+
+return ret ? ret : 2;
+}
+
  for (i = 0; i < num; i++) {
-ret = bcm2835_i2c_xfer_msg(i2c_dev, [i]);
+ret = bcm2835_i2c_xfer_msg(i2c_dev, [i], NULL);
  if (ret)
  break;
  }

This does not seem to implement the i2c_msg api correctly.

As per comments in include/uapi/linux/i2c.h on line 58 only the last
message
in a group should - by default - send a STOP.



Apparently it's a known problem that the i2c controller doesn't support
Repeated Start. It will always issue a Stop when it has transferred DLEN
bytes.
Refs:
http://www.circuitwizard.de/raspi-i2c-fix/raspi-i2c-fix.html
http://raspberrypi.stackexchange.com/questions/31728/has-anyone-successfully-used-i2c-repeated-starts-on-the-pi2-my-scope-says-they


UNLESS: a Start Transfer (ST) is issued after Transfer Active (TA) is set
and before DONE is set (or the last byte is shifted, I don't know excatly).
Refs:
https://github.com/raspberrypi/linux/issues/254#issuecomment-15254134
https://www.raspberrypi.org/forums/viewtopic.php?p=807834=2b612c7209f2175bf1a266359c72ae6c#p807834


I found this answer/report by joan that the downstream combined support
isn't reliable:
http://raspberrypi.stackexchange.com/questions/31728/has-anyone-successfully-used-i2c-repeated-starts-on-the-pi2-my-scope-says-they


My implementation differs from downstream in that I use local_irq_save()
to protect the polling loop. But that only protects from missing the TA
(downstream can miss the TA and issue a Stop).

So currently in mainline we have a driver that says it support the standard
(I2C_FUNC_I2C), but it really only supports one message transfers since it
can't do ReStart.

What I have done in this patch is to support ReStart for transfers with
2 messages: first write, then read. But maybe a better solution is to just
leave this alone if it is flaky and use bitbanging instead. I don't know.

I have not said that the approach you have taken is wrong or bad.

I was only telling you that the portion inside the bcm2835_i2c_xfer:
+   /* Combined write-read to the same address (smbus) */
+   if (num == 2 && (msgs[0].addr == msgs[1].addr) &&
+   !(msgs[0].flags & I2C_M_RD) && (msgs[1].flags & I2C_M_RD) &&
+   (msgs[0].len <= 16)) {
+   ret = bcm2835_i2c_xfer_msg(i2c_dev, [0], [1]);
+
+   return ret ? ret : 2;
+   }
is very specific and maybe could be done in a "generic" manner
supporting more cases.

At least add a dev_warn_once for all num > 1 cases not handled by the
code above.

This gives people an opportunity to detect such a situation if they
find something is not working as expected.

Martin

Re: [PATCH 2/3] i2c: bcm2835: Add support for combined write-read transfer

2016-09-20 Thread Noralf Trønnes



Den 20.09.2016 09:19, skrev Martin Sperl:

Hi Noralf!

On 19.09.2016 17:26, Noralf Trønnes wrote:

Some SMBus protocols use Repeated Start Condition to switch from write
mode to read mode. Devices like MMA8451 won't work without it.

When downstream implemented support for this in i2c-bcm2708, it broke
support for some devices, so a module parameter was added and combined
transfer was disabled by default.
See https://github.com/raspberrypi/linux/issues/599
It doesn't seem to have been any investigation into what the problem
really was. Later there was added a timeout on the polling loop.

One of the devices mentioned to partially stop working was DS1307.

I have run thousands of transfers to a DS1307 (rtc), MMA8451 (accel)
and AT24C32 (eeprom) in parallel without problems.

Signed-off-by: Noralf Trønnes 
---
  drivers/i2c/busses/i2c-bcm2835.c | 107 
+++

  1 file changed, 98 insertions(+), 9 deletions(-)

...
@@ -209,8 +289,17 @@ static int bcm2835_i2c_xfer(struct i2c_adapter 
*adap, struct i2c_msg msgs[],

  int i;
  int ret = 0;
  +/* Combined write-read to the same address (smbus) */
+if (num == 2 && (msgs[0].addr == msgs[1].addr) &&
+!(msgs[0].flags & I2C_M_RD) && (msgs[1].flags & I2C_M_RD) &&
+(msgs[0].len <= 16)) {
+ret = bcm2835_i2c_xfer_msg(i2c_dev, [0], [1]);
+
+return ret ? ret : 2;
+}
+
  for (i = 0; i < num; i++) {
-ret = bcm2835_i2c_xfer_msg(i2c_dev, [i]);
+ret = bcm2835_i2c_xfer_msg(i2c_dev, [i], NULL);
  if (ret)
  break;
  }

This does not seem to implement the i2c_msg api correctly.

As per comments in include/uapi/linux/i2c.h on line 58 only the last 
message

in a group should - by default - send a STOP.



Apparently it's a known problem that the i2c controller doesn't support
Repeated Start. It will always issue a Stop when it has transferred DLEN
bytes.
Refs:
http://www.circuitwizard.de/raspi-i2c-fix/raspi-i2c-fix.html
http://raspberrypi.stackexchange.com/questions/31728/has-anyone-successfully-used-i2c-repeated-starts-on-the-pi2-my-scope-says-they

UNLESS: a Start Transfer (ST) is issued after Transfer Active (TA) is set
and before DONE is set (or the last byte is shifted, I don't know excatly).
Refs:
https://github.com/raspberrypi/linux/issues/254#issuecomment-15254134
https://www.raspberrypi.org/forums/viewtopic.php?p=807834=2b612c7209f2175bf1a266359c72ae6c#p807834

I found this answer/report by joan that the downstream combined support
isn't reliable:
http://raspberrypi.stackexchange.com/questions/31728/has-anyone-successfully-used-i2c-repeated-starts-on-the-pi2-my-scope-says-they

My implementation differs from downstream in that I use local_irq_save()
to protect the polling loop. But that only protects from missing the TA
(downstream can miss the TA and issue a Stop).

So currently in mainline we have a driver that says it support the standard
(I2C_FUNC_I2C), but it really only supports one message transfers since it
can't do ReStart.

What I have done in this patch is to support ReStart for transfers with
2 messages: first write, then read. But maybe a better solution is to just
leave this alone if it is flaky and use bitbanging instead. I don't know.


Noralf.



As far as I understand  you would need to implement the I2C_M_STOP flag
(by exposing  I2C_FUNC_PROTOCOL_MANGLING in bcm2835_i2c_func)
to make this work correctly:

 for (i = 0; i < num; i++) {
+bool send_stop = (i == num - 1) ||msgs[i] 
->flags 
 _M_STOP 
;

-ret = bcm2835_i2c_xfer_msg(i2c_dev, [i]);
+ret = bcm2835_i2c_xfer_msg(i2c_dev, [i], send_stop);
 if (ret)
 break;
 }

The corresponding device driver (or userspace) will need to set the 
flag correctly.


Martin

Re: [PATCH 2/3] i2c: bcm2835: Add support for combined write-read transfer

2016-09-20 Thread Noralf Trønnes



Den 20.09.2016 09:19, skrev Martin Sperl:

Hi Noralf!

On 19.09.2016 17:26, Noralf Trønnes wrote:

Some SMBus protocols use Repeated Start Condition to switch from write
mode to read mode. Devices like MMA8451 won't work without it.

When downstream implemented support for this in i2c-bcm2708, it broke
support for some devices, so a module parameter was added and combined
transfer was disabled by default.
See https://github.com/raspberrypi/linux/issues/599
It doesn't seem to have been any investigation into what the problem
really was. Later there was added a timeout on the polling loop.

One of the devices mentioned to partially stop working was DS1307.

I have run thousands of transfers to a DS1307 (rtc), MMA8451 (accel)
and AT24C32 (eeprom) in parallel without problems.

Signed-off-by: Noralf Trønnes 
---
  drivers/i2c/busses/i2c-bcm2835.c | 107 
+++

  1 file changed, 98 insertions(+), 9 deletions(-)

...
@@ -209,8 +289,17 @@ static int bcm2835_i2c_xfer(struct i2c_adapter 
*adap, struct i2c_msg msgs[],

  int i;
  int ret = 0;
  +/* Combined write-read to the same address (smbus) */
+if (num == 2 && (msgs[0].addr == msgs[1].addr) &&
+!(msgs[0].flags & I2C_M_RD) && (msgs[1].flags & I2C_M_RD) &&
+(msgs[0].len <= 16)) {
+ret = bcm2835_i2c_xfer_msg(i2c_dev, [0], [1]);
+
+return ret ? ret : 2;
+}
+
  for (i = 0; i < num; i++) {
-ret = bcm2835_i2c_xfer_msg(i2c_dev, [i]);
+ret = bcm2835_i2c_xfer_msg(i2c_dev, [i], NULL);
  if (ret)
  break;
  }

This does not seem to implement the i2c_msg api correctly.

As per comments in include/uapi/linux/i2c.h on line 58 only the last 
message

in a group should - by default - send a STOP.



Apparently it's a known problem that the i2c controller doesn't support
Repeated Start. It will always issue a Stop when it has transferred DLEN
bytes.
Refs:
http://www.circuitwizard.de/raspi-i2c-fix/raspi-i2c-fix.html
http://raspberrypi.stackexchange.com/questions/31728/has-anyone-successfully-used-i2c-repeated-starts-on-the-pi2-my-scope-says-they

UNLESS: a Start Transfer (ST) is issued after Transfer Active (TA) is set
and before DONE is set (or the last byte is shifted, I don't know excatly).
Refs:
https://github.com/raspberrypi/linux/issues/254#issuecomment-15254134
https://www.raspberrypi.org/forums/viewtopic.php?p=807834=2b612c7209f2175bf1a266359c72ae6c#p807834

I found this answer/report by joan that the downstream combined support
isn't reliable:
http://raspberrypi.stackexchange.com/questions/31728/has-anyone-successfully-used-i2c-repeated-starts-on-the-pi2-my-scope-says-they

My implementation differs from downstream in that I use local_irq_save()
to protect the polling loop. But that only protects from missing the TA
(downstream can miss the TA and issue a Stop).

So currently in mainline we have a driver that says it support the standard
(I2C_FUNC_I2C), but it really only supports one message transfers since it
can't do ReStart.

What I have done in this patch is to support ReStart for transfers with
2 messages: first write, then read. But maybe a better solution is to just
leave this alone if it is flaky and use bitbanging instead. I don't know.


Noralf.



As far as I understand  you would need to implement the I2C_M_STOP flag
(by exposing  I2C_FUNC_PROTOCOL_MANGLING in bcm2835_i2c_func)
to make this work correctly:

 for (i = 0; i < num; i++) {
+bool send_stop = (i == num - 1) ||msgs[i] 
->flags 
 _M_STOP 
;

-ret = bcm2835_i2c_xfer_msg(i2c_dev, [i]);
+ret = bcm2835_i2c_xfer_msg(i2c_dev, [i], send_stop);
 if (ret)
 break;
 }

The corresponding device driver (or userspace) will need to set the 
flag correctly.


Martin

Re: [PATCH 2/3] i2c: bcm2835: Add support for combined write-read transfer

2016-09-20 Thread Martin Sperl


Hi Noralf!

On 19.09.2016 17:26, Noralf Trønnes wrote:

Some SMBus protocols use Repeated Start Condition to switch from write
mode to read mode. Devices like MMA8451 won't work without it.

When downstream implemented support for this in i2c-bcm2708, it broke
support for some devices, so a module parameter was added and combined
transfer was disabled by default.
See https://github.com/raspberrypi/linux/issues/599
It doesn't seem to have been any investigation into what the problem
really was. Later there was added a timeout on the polling loop.

One of the devices mentioned to partially stop working was DS1307.

I have run thousands of transfers to a DS1307 (rtc), MMA8451 (accel)
and AT24C32 (eeprom) in parallel without problems.

Signed-off-by: Noralf Trønnes 
---
  drivers/i2c/busses/i2c-bcm2835.c | 107 +++
  1 file changed, 98 insertions(+), 9 deletions(-)

...

@@ -209,8 +289,17 @@ static int bcm2835_i2c_xfer(struct i2c_adapter *adap, 
struct i2c_msg msgs[],
int i;
int ret = 0;
  
+	/* Combined write-read to the same address (smbus) */

+   if (num == 2 && (msgs[0].addr == msgs[1].addr) &&
+   !(msgs[0].flags & I2C_M_RD) && (msgs[1].flags & I2C_M_RD) &&
+   (msgs[0].len <= 16)) {
+   ret = bcm2835_i2c_xfer_msg(i2c_dev, [0], [1]);
+
+   return ret ? ret : 2;
+   }
+
for (i = 0; i < num; i++) {
-   ret = bcm2835_i2c_xfer_msg(i2c_dev, [i]);
+   ret = bcm2835_i2c_xfer_msg(i2c_dev, [i], NULL);
if (ret)
break;
}

This does not seem to implement the i2c_msg api correctly.

As per comments in include/uapi/linux/i2c.h on line 58 only the last message
in a group should - by default - send a STOP.

As far as I understand  you would need to implement the I2C_M_STOP flag
(by exposing  I2C_FUNC_PROTOCOL_MANGLING in bcm2835_i2c_func)
to make this work correctly:

for (i = 0; i < num; i++) {
+   bool send_stop = (i == num - 1) ||msgs[i] 
->flags 
  _M_STOP 
;
-   ret = bcm2835_i2c_xfer_msg(i2c_dev, [i]);
+   ret = bcm2835_i2c_xfer_msg(i2c_dev, [i], send_stop);
if (ret)
break;
}

The corresponding device driver (or userspace) will need to set the flag 
correctly.


Martin

Re: [PATCH 2/3] i2c: bcm2835: Add support for combined write-read transfer

2016-09-20 Thread Martin Sperl


Hi Noralf!

On 19.09.2016 17:26, Noralf Trønnes wrote:

Some SMBus protocols use Repeated Start Condition to switch from write
mode to read mode. Devices like MMA8451 won't work without it.

When downstream implemented support for this in i2c-bcm2708, it broke
support for some devices, so a module parameter was added and combined
transfer was disabled by default.
See https://github.com/raspberrypi/linux/issues/599
It doesn't seem to have been any investigation into what the problem
really was. Later there was added a timeout on the polling loop.

One of the devices mentioned to partially stop working was DS1307.

I have run thousands of transfers to a DS1307 (rtc), MMA8451 (accel)
and AT24C32 (eeprom) in parallel without problems.

Signed-off-by: Noralf Trønnes 
---
  drivers/i2c/busses/i2c-bcm2835.c | 107 +++
  1 file changed, 98 insertions(+), 9 deletions(-)

...

@@ -209,8 +289,17 @@ static int bcm2835_i2c_xfer(struct i2c_adapter *adap, 
struct i2c_msg msgs[],
int i;
int ret = 0;
  
+	/* Combined write-read to the same address (smbus) */

+   if (num == 2 && (msgs[0].addr == msgs[1].addr) &&
+   !(msgs[0].flags & I2C_M_RD) && (msgs[1].flags & I2C_M_RD) &&
+   (msgs[0].len <= 16)) {
+   ret = bcm2835_i2c_xfer_msg(i2c_dev, [0], [1]);
+
+   return ret ? ret : 2;
+   }
+
for (i = 0; i < num; i++) {
-   ret = bcm2835_i2c_xfer_msg(i2c_dev, [i]);
+   ret = bcm2835_i2c_xfer_msg(i2c_dev, [i], NULL);
if (ret)
break;
}

This does not seem to implement the i2c_msg api correctly.

As per comments in include/uapi/linux/i2c.h on line 58 only the last message
in a group should - by default - send a STOP.

As far as I understand  you would need to implement the I2C_M_STOP flag
(by exposing  I2C_FUNC_PROTOCOL_MANGLING in bcm2835_i2c_func)
to make this work correctly:

for (i = 0; i < num; i++) {
+   bool send_stop = (i == num - 1) ||msgs[i] 
->flags 
  _M_STOP 
;
-   ret = bcm2835_i2c_xfer_msg(i2c_dev, [i]);
+   ret = bcm2835_i2c_xfer_msg(i2c_dev, [i], send_stop);
if (ret)
break;
}

The corresponding device driver (or userspace) will need to set the flag 
correctly.


Martin

[PATCH 2/3] i2c: bcm2835: Add support for combined write-read transfer

2016-09-19 Thread Noralf Trønnes

Some SMBus protocols use Repeated Start Condition to switch from write
mode to read mode. Devices like MMA8451 won't work without it.

When downstream implemented support for this in i2c-bcm2708, it broke
support for some devices, so a module parameter was added and combined
transfer was disabled by default.
See https://github.com/raspberrypi/linux/issues/599
It doesn't seem to have been any investigation into what the problem
really was. Later there was added a timeout on the polling loop.

One of the devices mentioned to partially stop working was DS1307.

I have run thousands of transfers to a DS1307 (rtc), MMA8451 (accel)
and AT24C32 (eeprom) in parallel without problems.

Signed-off-by: Noralf Trønnes 
---
 drivers/i2c/busses/i2c-bcm2835.c | 107 +++
 1 file changed, 98 insertions(+), 9 deletions(-)

diff --git a/drivers/i2c/busses/i2c-bcm2835.c b/drivers/i2c/busses/i2c-bcm2835.c
index f283b71..b3ce565 100644
--- a/drivers/i2c/busses/i2c-bcm2835.c
+++ b/drivers/i2c/busses/i2c-bcm2835.c
@@ -154,8 +154,39 @@ static irqreturn_t bcm2835_i2c_isr(int this_irq, void 
*data)
return IRQ_NONE;
 }
 
+/*
+ * Repeated Start Condition (Sr)
+ * The BCM2835 ARM Peripherals datasheet mentions a way to trigger a Sr when it
+ * talks about reading from a slave with 10 bit address. This is achieved by
+ * issuing a write (without enabling interrupts), poll the I2CS.TA flag and
+ * wait for it to be set, and then issue a read.
+ * https://github.com/raspberrypi/linux/issues/254 shows how the firmware does
+ * it and states that it's a workaround for a problem in the state machine.
+ * This is the comment in the firmware code:
+ *
+ * The I2C peripheral samples the values for rw_bit and xfer_count in the
+ * IDLE state if start is set.
+ *
+ * We want to generate a ReSTART not a STOP at the end of the TX phase. In
+ * order to do that we must ensure the state machine goes
+ * RACK1 -> RACK2 -> SRSTRT1 (not RACK1 -> RACK2 -> SSTOP1).
+ *
+ * So, in the RACK2 state when (TX) xfer_count==0 we must therefore have
+ * already set, ready to be sampled:
+ * READ; rw_bit <= I2CC bit 0 - must be "read"
+ * ST;   start  <= I2CC bit 7 - must be "Go" in order to not issue STOP
+ * DLEN; xfer_count <= I2CDLEN- must be equal to our read amount
+ *
+ * The plan to do this is:
+ * 1. Start the sub-address write, but don't let it finish (keep
+ *xfer_count > 0)
+ * 2. Populate READ, DLEN and ST in preparation for ReSTART read sequence
+ * 3. Let TX finish (write the rest of the data)
+ * 4. Read back data as it arrives
+ */
+
 static int bcm2835_i2c_xfer_msg(struct bcm2835_i2c_dev *i2c_dev,
-   struct i2c_msg *msg)
+   struct i2c_msg *msg, struct i2c_msg *msg2)
 {
u32 c;
unsigned long time_left;
@@ -167,21 +198,70 @@ static int bcm2835_i2c_xfer_msg(struct bcm2835_i2c_dev 
*i2c_dev,
 
bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_C, BCM2835_I2C_C_CLEAR);
 
-   if (msg->flags & I2C_M_RD) {
-   c = BCM2835_I2C_C_READ | BCM2835_I2C_C_INTR;
-   } else {
-   c = BCM2835_I2C_C_INTT;
+   if (!(msg->flags & I2C_M_RD))
bcm2835_fill_txfifo(i2c_dev);
-   }
-   c |= BCM2835_I2C_C_ST | BCM2835_I2C_C_INTD | BCM2835_I2C_C_I2CEN;
 
bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_A, msg->addr);
bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_DLEN, msg->len);
-   bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_C, c);
+
+   if (!msg2) {
+   if (msg->flags & I2C_M_RD)
+   c = BCM2835_I2C_C_READ | BCM2835_I2C_C_INTR;
+   else
+   c = BCM2835_I2C_C_INTT;
+
+   c |= BCM2835_I2C_C_ST | BCM2835_I2C_C_INTD |
+BCM2835_I2C_C_I2CEN;
+   bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_C, c);
+   } else {
+   unsigned long flags;
+   u32 stat, err = 0;
+
+   local_irq_save(flags);
+
+   /* Start write message */
+   c = BCM2835_I2C_C_ST | BCM2835_I2C_C_I2CEN;
+   bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_C, c);
+
+   /* Wait for the transfer to become active */
+   for (time_left = 100; time_left > 0; time_left--) {
+   stat = bcm2835_i2c_readl(i2c_dev, BCM2835_I2C_S);
+
+   err = stat & (BCM2835_I2C_S_CLKT | BCM2835_I2C_S_ERR);
+   if (err)
+   break;
+
+   if (stat & BCM2835_I2C_S_TA)
+   break;
+   }
+
+   if (err || !time_left) {
+   i2c_dev->msg_err = err;
+   local_irq_restore(flags);
+   goto error;
+   }
+
+   /* Start read message */
+

[PATCH 2/3] i2c: bcm2835: Add support for combined write-read transfer

2016-09-19 Thread Noralf Trønnes

Some SMBus protocols use Repeated Start Condition to switch from write
mode to read mode. Devices like MMA8451 won't work without it.

When downstream implemented support for this in i2c-bcm2708, it broke
support for some devices, so a module parameter was added and combined
transfer was disabled by default.
See https://github.com/raspberrypi/linux/issues/599
It doesn't seem to have been any investigation into what the problem
really was. Later there was added a timeout on the polling loop.

One of the devices mentioned to partially stop working was DS1307.

I have run thousands of transfers to a DS1307 (rtc), MMA8451 (accel)
and AT24C32 (eeprom) in parallel without problems.

Signed-off-by: Noralf Trønnes 
---
 drivers/i2c/busses/i2c-bcm2835.c | 107 +++
 1 file changed, 98 insertions(+), 9 deletions(-)

diff --git a/drivers/i2c/busses/i2c-bcm2835.c b/drivers/i2c/busses/i2c-bcm2835.c
index f283b71..b3ce565 100644
--- a/drivers/i2c/busses/i2c-bcm2835.c
+++ b/drivers/i2c/busses/i2c-bcm2835.c
@@ -154,8 +154,39 @@ static irqreturn_t bcm2835_i2c_isr(int this_irq, void 
*data)
return IRQ_NONE;
 }
 
+/*
+ * Repeated Start Condition (Sr)
+ * The BCM2835 ARM Peripherals datasheet mentions a way to trigger a Sr when it
+ * talks about reading from a slave with 10 bit address. This is achieved by
+ * issuing a write (without enabling interrupts), poll the I2CS.TA flag and
+ * wait for it to be set, and then issue a read.
+ * https://github.com/raspberrypi/linux/issues/254 shows how the firmware does
+ * it and states that it's a workaround for a problem in the state machine.
+ * This is the comment in the firmware code:
+ *
+ * The I2C peripheral samples the values for rw_bit and xfer_count in the
+ * IDLE state if start is set.
+ *
+ * We want to generate a ReSTART not a STOP at the end of the TX phase. In
+ * order to do that we must ensure the state machine goes
+ * RACK1 -> RACK2 -> SRSTRT1 (not RACK1 -> RACK2 -> SSTOP1).
+ *
+ * So, in the RACK2 state when (TX) xfer_count==0 we must therefore have
+ * already set, ready to be sampled:
+ * READ; rw_bit <= I2CC bit 0 - must be "read"
+ * ST;   start  <= I2CC bit 7 - must be "Go" in order to not issue STOP
+ * DLEN; xfer_count <= I2CDLEN- must be equal to our read amount
+ *
+ * The plan to do this is:
+ * 1. Start the sub-address write, but don't let it finish (keep
+ *xfer_count > 0)
+ * 2. Populate READ, DLEN and ST in preparation for ReSTART read sequence
+ * 3. Let TX finish (write the rest of the data)
+ * 4. Read back data as it arrives
+ */
+
 static int bcm2835_i2c_xfer_msg(struct bcm2835_i2c_dev *i2c_dev,
-   struct i2c_msg *msg)
+   struct i2c_msg *msg, struct i2c_msg *msg2)
 {
u32 c;
unsigned long time_left;
@@ -167,21 +198,70 @@ static int bcm2835_i2c_xfer_msg(struct bcm2835_i2c_dev 
*i2c_dev,
 
bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_C, BCM2835_I2C_C_CLEAR);
 
-   if (msg->flags & I2C_M_RD) {
-   c = BCM2835_I2C_C_READ | BCM2835_I2C_C_INTR;
-   } else {
-   c = BCM2835_I2C_C_INTT;
+   if (!(msg->flags & I2C_M_RD))
bcm2835_fill_txfifo(i2c_dev);
-   }
-   c |= BCM2835_I2C_C_ST | BCM2835_I2C_C_INTD | BCM2835_I2C_C_I2CEN;
 
bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_A, msg->addr);
bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_DLEN, msg->len);
-   bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_C, c);
+
+   if (!msg2) {
+   if (msg->flags & I2C_M_RD)
+   c = BCM2835_I2C_C_READ | BCM2835_I2C_C_INTR;
+   else
+   c = BCM2835_I2C_C_INTT;
+
+   c |= BCM2835_I2C_C_ST | BCM2835_I2C_C_INTD |
+BCM2835_I2C_C_I2CEN;
+   bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_C, c);
+   } else {
+   unsigned long flags;
+   u32 stat, err = 0;
+
+   local_irq_save(flags);
+
+   /* Start write message */
+   c = BCM2835_I2C_C_ST | BCM2835_I2C_C_I2CEN;
+   bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_C, c);
+
+   /* Wait for the transfer to become active */
+   for (time_left = 100; time_left > 0; time_left--) {
+   stat = bcm2835_i2c_readl(i2c_dev, BCM2835_I2C_S);
+
+   err = stat & (BCM2835_I2C_S_CLKT | BCM2835_I2C_S_ERR);
+   if (err)
+   break;
+
+   if (stat & BCM2835_I2C_S_TA)
+   break;
+   }
+
+   if (err || !time_left) {
+   i2c_dev->msg_err = err;
+   local_irq_restore(flags);
+   goto error;
+   }
+
+   /* Start read message */
+   i2c_dev->curr_msg = msg2;

Re: [PATCH 2/3] i2c: bcm2835: Add support for combined write-read transfer

Re: [PATCH 2/3] i2c: bcm2835: Add support for combined write-read transfer

Re: [PATCH 2/3] i2c: bcm2835: Add support for combined write-read transfer

Re: [PATCH 2/3] i2c: bcm2835: Add support for combined write-read transfer

Re: [PATCH 2/3] i2c: bcm2835: Add support for combined write-read transfer

Re: [PATCH 2/3] i2c: bcm2835: Add support for combined write-read transfer

Re: [PATCH 2/3] i2c: bcm2835: Add support for combined write-read transfer

Re: [PATCH 2/3] i2c: bcm2835: Add support for combined write-read transfer

Re: [PATCH 2/3] i2c: bcm2835: Add support for combined write-read transfer

Re: [PATCH 2/3] i2c: bcm2835: Add support for combined write-read transfer

Re: [PATCH 2/3] i2c: bcm2835: Add support for combined write-read transfer

Re: [PATCH 2/3] i2c: bcm2835: Add support for combined write-read transfer

[PATCH 2/3] i2c: bcm2835: Add support for combined write-read transfer

[PATCH 2/3] i2c: bcm2835: Add support for combined write-read transfer

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