Re: [PATCH 1/3] i2c: bcm2835: Fix hang for writing messages larger than 16 bytes

[Martin Sperl]

On 19.09.2016 17:26, Noralf Trønnes wrote:

Writing messages larger than the FIFO size results in a hang, rendering
the machine unusable. This is because the RXD status flag is set on the
first interrupt which results in bcm2835_drain_rxfifo() stealing bytes
from the buffer. The controller continues to trigger interrupts waiting
for the missing bytes, but bcm2835_fill_txfifo() has none to give.

I remember having seen similar interrupt issues with the SPI HW-block.

In this situation wait_for_completion_timeout() apparently is unable to
stop the madness.
That is because it is a level irq that immediately triggers another 
interrupt giving

no CPU no time to do other (threaded) OS activity - this might be slightly
different for multi-core machines...

The BCM2835 ARM Peripherals datasheet has this to say about the flags:
   TXD: is set when the FIFO has space for at least one byte of data.
   RXD: is set when the FIFO contains at least one byte of data.
   TXW: is set during a write transfer and the FIFO is less than full.
   RXR: is set during a read transfer and the FIFO is or more full.

Implementing the logic from the downstream i2c-bcm2708 driver solved
the hang problem.

Signed-off-by: Noralf Trønnes

Reviewed-by: Martin Sperl 

Re: [PATCH 1/3] i2c: bcm2835: Fix hang for writing messages larger than 16 bytes

[Martin Sperl]

On 19.09.2016 17:26, Noralf Trønnes wrote:

Writing messages larger than the FIFO size results in a hang, rendering
the machine unusable. This is because the RXD status flag is set on the
first interrupt which results in bcm2835_drain_rxfifo() stealing bytes
from the buffer. The controller continues to trigger interrupts waiting
for the missing bytes, but bcm2835_fill_txfifo() has none to give.

I remember having seen similar interrupt issues with the SPI HW-block.

In this situation wait_for_completion_timeout() apparently is unable to
stop the madness.
That is because it is a level irq that immediately triggers another 
interrupt giving

no CPU no time to do other (threaded) OS activity - this might be slightly
different for multi-core machines...

The BCM2835 ARM Peripherals datasheet has this to say about the flags:
   TXD: is set when the FIFO has space for at least one byte of data.
   RXD: is set when the FIFO contains at least one byte of data.
   TXW: is set during a write transfer and the FIFO is less than full.
   RXR: is set during a read transfer and the FIFO is or more full.

Implementing the logic from the downstream i2c-bcm2708 driver solved
the hang problem.

Signed-off-by: Noralf Trønnes

Reviewed-by: Martin Sperl 

Re: [PATCH 1/3] i2c: bcm2835: Fix hang for writing messages larger than 16 bytes

[Noralf Trønnes]

Den 19.09.2016 18:51, skrev Eric Anholt:

Noralf Trønnes  writes:


Writing messages larger than the FIFO size results in a hang, rendering
the machine unusable. This is because the RXD status flag is set on the
first interrupt which results in bcm2835_drain_rxfifo() stealing bytes
from the buffer. The controller continues to trigger interrupts waiting
for the missing bytes, but bcm2835_fill_txfifo() has none to give.
In this situation wait_for_completion_timeout() apparently is unable to
stop the madness.

The BCM2835 ARM Peripherals datasheet has this to say about the flags:
   TXD: is set when the FIFO has space for at least one byte of data.
   RXD: is set when the FIFO contains at least one byte of data.
   TXW: is set during a write transfer and the FIFO is less than full.
   RXR: is set during a read transfer and the FIFO is or more full.

Implementing the logic from the downstream i2c-bcm2708 driver solved
the hang problem.

Signed-off-by: Noralf Trønnes 

Patches 1, 3 are:

Reviewed-by: Eric Anholt 

For patch 2 I followed some of it, but couldn't quite say it's a review.
I trust your testing, and that the path has had a lot more testing in
the downstream tree, so it's:


I don't know how much testing downstream really has had since this feature
is disabled by default. So there is a possibility that this can break some
devices (while at the same time enable others).
I wondered about adding a module parameter so it could be disabled at
runtime, but decided to see what the review would be first.
It is of course possible to add a this module parameter later should it
turn out to break some device.

Noralf.


Acked-by: Eric Anholt 

Thanks!

Re: [PATCH 1/3] i2c: bcm2835: Fix hang for writing messages larger than 16 bytes

[Noralf Trønnes]

Den 19.09.2016 18:51, skrev Eric Anholt:

Noralf Trønnes  writes:


Writing messages larger than the FIFO size results in a hang, rendering
the machine unusable. This is because the RXD status flag is set on the
first interrupt which results in bcm2835_drain_rxfifo() stealing bytes
from the buffer. The controller continues to trigger interrupts waiting
for the missing bytes, but bcm2835_fill_txfifo() has none to give.
In this situation wait_for_completion_timeout() apparently is unable to
stop the madness.

The BCM2835 ARM Peripherals datasheet has this to say about the flags:
   TXD: is set when the FIFO has space for at least one byte of data.
   RXD: is set when the FIFO contains at least one byte of data.
   TXW: is set during a write transfer and the FIFO is less than full.
   RXR: is set during a read transfer and the FIFO is or more full.

Implementing the logic from the downstream i2c-bcm2708 driver solved
the hang problem.

Signed-off-by: Noralf Trønnes 

Patches 1, 3 are:

Reviewed-by: Eric Anholt 

For patch 2 I followed some of it, but couldn't quite say it's a review.
I trust your testing, and that the path has had a lot more testing in
the downstream tree, so it's:


I don't know how much testing downstream really has had since this feature
is disabled by default. So there is a possibility that this can break some
devices (while at the same time enable others).
I wondered about adding a module parameter so it could be disabled at
runtime, but decided to see what the review would be first.
It is of course possible to add a this module parameter later should it
turn out to break some device.

Noralf.


Acked-by: Eric Anholt 

Thanks!

Re: [PATCH 1/3] i2c: bcm2835: Fix hang for writing messages larger than 16 bytes

[Eric Anholt]

Noralf Trønnes  writes:

> Writing messages larger than the FIFO size results in a hang, rendering
> the machine unusable. This is because the RXD status flag is set on the
> first interrupt which results in bcm2835_drain_rxfifo() stealing bytes
> from the buffer. The controller continues to trigger interrupts waiting
> for the missing bytes, but bcm2835_fill_txfifo() has none to give.
> In this situation wait_for_completion_timeout() apparently is unable to
> stop the madness.
>
> The BCM2835 ARM Peripherals datasheet has this to say about the flags:
>   TXD: is set when the FIFO has space for at least one byte of data.
>   RXD: is set when the FIFO contains at least one byte of data.
>   TXW: is set during a write transfer and the FIFO is less than full.
>   RXR: is set during a read transfer and the FIFO is or more full.
>
> Implementing the logic from the downstream i2c-bcm2708 driver solved
> the hang problem.
>
> Signed-off-by: Noralf Trønnes 

Patches 1, 3 are:

Reviewed-by: Eric Anholt 

For patch 2 I followed some of it, but couldn't quite say it's a review.
I trust your testing, and that the path has had a lot more testing in
the downstream tree, so it's:

Acked-by: Eric Anholt 

Thanks!


signature.asc
Description: PGP signature

Re: [PATCH 1/3] i2c: bcm2835: Fix hang for writing messages larger than 16 bytes

[Eric Anholt]

Noralf Trønnes  writes:

> Writing messages larger than the FIFO size results in a hang, rendering
> the machine unusable. This is because the RXD status flag is set on the
> first interrupt which results in bcm2835_drain_rxfifo() stealing bytes
> from the buffer. The controller continues to trigger interrupts waiting
> for the missing bytes, but bcm2835_fill_txfifo() has none to give.
> In this situation wait_for_completion_timeout() apparently is unable to
> stop the madness.
>
> The BCM2835 ARM Peripherals datasheet has this to say about the flags:
>   TXD: is set when the FIFO has space for at least one byte of data.
>   RXD: is set when the FIFO contains at least one byte of data.
>   TXW: is set during a write transfer and the FIFO is less than full.
>   RXR: is set during a read transfer and the FIFO is or more full.
>
> Implementing the logic from the downstream i2c-bcm2708 driver solved
> the hang problem.
>
> Signed-off-by: Noralf Trønnes 

Patches 1, 3 are:

Reviewed-by: Eric Anholt 

For patch 2 I followed some of it, but couldn't quite say it's a review.
I trust your testing, and that the path has had a lot more testing in
the downstream tree, so it's:

Acked-by: Eric Anholt 

Thanks!


signature.asc
Description: PGP signature

[PATCH 1/3] i2c: bcm2835: Fix hang for writing messages larger than 16 bytes

[Noralf Trønnes]

Writing messages larger than the FIFO size results in a hang, rendering
the machine unusable. This is because the RXD status flag is set on the
first interrupt which results in bcm2835_drain_rxfifo() stealing bytes
from the buffer. The controller continues to trigger interrupts waiting
for the missing bytes, but bcm2835_fill_txfifo() has none to give.
In this situation wait_for_completion_timeout() apparently is unable to
stop the madness.

The BCM2835 ARM Peripherals datasheet has this to say about the flags:
  TXD: is set when the FIFO has space for at least one byte of data.
  RXD: is set when the FIFO contains at least one byte of data.
  TXW: is set during a write transfer and the FIFO is less than full.
  RXR: is set during a read transfer and the FIFO is or more full.

Implementing the logic from the downstream i2c-bcm2708 driver solved
the hang problem.

Signed-off-by: Noralf Trønnes 
---
 drivers/i2c/busses/i2c-bcm2835.c | 22 ++
 1 file changed, 14 insertions(+), 8 deletions(-)

diff --git a/drivers/i2c/busses/i2c-bcm2835.c b/drivers/i2c/busses/i2c-bcm2835.c
index d4f3239..f283b71 100644
--- a/drivers/i2c/busses/i2c-bcm2835.c
+++ b/drivers/i2c/busses/i2c-bcm2835.c
@@ -64,6 +64,7 @@ struct bcm2835_i2c_dev {
int irq;
struct i2c_adapter adapter;
struct completion completion;
+   struct i2c_msg *curr_msg;
u32 msg_err;
u8 *msg_buf;
size_t msg_buf_remaining;
@@ -126,14 +127,13 @@ static irqreturn_t bcm2835_i2c_isr(int this_irq, void 
*data)
return IRQ_HANDLED;
}
 
-   if (val & BCM2835_I2C_S_RXD) {
-   bcm2835_drain_rxfifo(i2c_dev);
-   if (!(val & BCM2835_I2C_S_DONE))
-   return IRQ_HANDLED;
-   }
-
if (val & BCM2835_I2C_S_DONE) {
-   if (i2c_dev->msg_buf_remaining)
+   if (i2c_dev->curr_msg->flags & I2C_M_RD) {
+   bcm2835_drain_rxfifo(i2c_dev);
+   val = bcm2835_i2c_readl(i2c_dev, BCM2835_I2C_S);
+   }
+
+   if ((val & BCM2835_I2C_S_RXD) || i2c_dev->msg_buf_remaining)
i2c_dev->msg_err = BCM2835_I2C_S_LEN;
else
i2c_dev->msg_err = 0;
@@ -141,11 +141,16 @@ static irqreturn_t bcm2835_i2c_isr(int this_irq, void 
*data)
return IRQ_HANDLED;
}
 
-   if (val & BCM2835_I2C_S_TXD) {
+   if (val & BCM2835_I2C_S_TXW) {
bcm2835_fill_txfifo(i2c_dev);
return IRQ_HANDLED;
}
 
+   if (val & BCM2835_I2C_S_RXR) {
+   bcm2835_drain_rxfifo(i2c_dev);
+   return IRQ_HANDLED;
+   }
+
return IRQ_NONE;
 }
 
@@ -155,6 +160,7 @@ static int bcm2835_i2c_xfer_msg(struct bcm2835_i2c_dev 
*i2c_dev,
u32 c;
unsigned long time_left;
 
+   i2c_dev->curr_msg = msg;
i2c_dev->msg_buf = msg->buf;
i2c_dev->msg_buf_remaining = msg->len;
reinit_completion(_dev->completion);
-- 
2.8.2

[PATCH 1/3] i2c: bcm2835: Fix hang for writing messages larger than 16 bytes

[Noralf Trønnes]

Writing messages larger than the FIFO size results in a hang, rendering
the machine unusable. This is because the RXD status flag is set on the
first interrupt which results in bcm2835_drain_rxfifo() stealing bytes
from the buffer. The controller continues to trigger interrupts waiting
for the missing bytes, but bcm2835_fill_txfifo() has none to give.
In this situation wait_for_completion_timeout() apparently is unable to
stop the madness.

The BCM2835 ARM Peripherals datasheet has this to say about the flags:
  TXD: is set when the FIFO has space for at least one byte of data.
  RXD: is set when the FIFO contains at least one byte of data.
  TXW: is set during a write transfer and the FIFO is less than full.
  RXR: is set during a read transfer and the FIFO is or more full.

Implementing the logic from the downstream i2c-bcm2708 driver solved
the hang problem.

Signed-off-by: Noralf Trønnes 
---
 drivers/i2c/busses/i2c-bcm2835.c | 22 ++
 1 file changed, 14 insertions(+), 8 deletions(-)

diff --git a/drivers/i2c/busses/i2c-bcm2835.c b/drivers/i2c/busses/i2c-bcm2835.c
index d4f3239..f283b71 100644
--- a/drivers/i2c/busses/i2c-bcm2835.c
+++ b/drivers/i2c/busses/i2c-bcm2835.c
@@ -64,6 +64,7 @@ struct bcm2835_i2c_dev {
int irq;
struct i2c_adapter adapter;
struct completion completion;
+   struct i2c_msg *curr_msg;
u32 msg_err;
u8 *msg_buf;
size_t msg_buf_remaining;
@@ -126,14 +127,13 @@ static irqreturn_t bcm2835_i2c_isr(int this_irq, void 
*data)
return IRQ_HANDLED;
}
 
-   if (val & BCM2835_I2C_S_RXD) {
-   bcm2835_drain_rxfifo(i2c_dev);
-   if (!(val & BCM2835_I2C_S_DONE))
-   return IRQ_HANDLED;
-   }
-
if (val & BCM2835_I2C_S_DONE) {
-   if (i2c_dev->msg_buf_remaining)
+   if (i2c_dev->curr_msg->flags & I2C_M_RD) {
+   bcm2835_drain_rxfifo(i2c_dev);
+   val = bcm2835_i2c_readl(i2c_dev, BCM2835_I2C_S);
+   }
+
+   if ((val & BCM2835_I2C_S_RXD) || i2c_dev->msg_buf_remaining)
i2c_dev->msg_err = BCM2835_I2C_S_LEN;
else
i2c_dev->msg_err = 0;
@@ -141,11 +141,16 @@ static irqreturn_t bcm2835_i2c_isr(int this_irq, void 
*data)
return IRQ_HANDLED;
}
 
-   if (val & BCM2835_I2C_S_TXD) {
+   if (val & BCM2835_I2C_S_TXW) {
bcm2835_fill_txfifo(i2c_dev);
return IRQ_HANDLED;
}
 
+   if (val & BCM2835_I2C_S_RXR) {
+   bcm2835_drain_rxfifo(i2c_dev);
+   return IRQ_HANDLED;
+   }
+
return IRQ_NONE;
 }
 
@@ -155,6 +160,7 @@ static int bcm2835_i2c_xfer_msg(struct bcm2835_i2c_dev 
*i2c_dev,
u32 c;
unsigned long time_left;
 
+   i2c_dev->curr_msg = msg;
i2c_dev->msg_buf = msg->buf;
i2c_dev->msg_buf_remaining = msg->len;
reinit_completion(_dev->completion);
-- 
2.8.2