Re: [U-Boot] A question about unconfigured pads check in omap24xx_i2c
On 11/08/2013 11:26 PM, Lubomir Popov wrote:
Hi Nikita,
On 11/06/2013 03:19 PM, Lubomir Popov wrote:
On 06-Nov-13 14:12, Nikita Kiryanov wrote:
In drivers/i2c/omap24xx_i2c.c there are a few checks that attempt to
detect unconfigured pads for the i2c bus in use. These checks are
all in the form of
if (status == I2C_STAT_XRDY) {
printf(unconfigured pads\n);
return -1;
}
This check seems peculiar to me since the meaning of I2C_STAT_XRDY is
that new data is requested for transmission. Why is that indication that
the bus is not padconf'd for I2C?
Hi Nikita,
This has been empirically confirmed on OMAP4 and OMAP5. When the pads
are not
configured, the I2C controller is actually disconnected from the bus.
The clock
input for its state machine has to come from the bus however due to
stretching
etc., although it is internally generated. So actually nothing changes
within
the controller after a transaction attempt is made, and it keeps its
initial
state with XRDY set only (ready to accept transmit data). I use this as an
indicator. Not perfect, but works in most cases.
Regards,
Lubo
Thanks for the quick reply.
The reason I stumbled across this is that this check hasn't been working
well on our OMAP3 based devices. Some I2C transactions work fine, but
some of them fail this check in the address phase, especially if the I2C
transactions happen in quick successions.
You mean that you occasionally get this error on an otherwise properly
configured and working bus, right?
Yes.
Does this happen with particular
slave devices only, or randomly? And is it happening in the SPL, or in
regular U-Boot?
It happens in U-Boot when communicating with the PMIC (TPS65930),
but like I said, it worked in the driver's previous version, on the
same module.
We did not have any I2C issues
with the previous driver, and while this behavior is symptomatic of
timing issues playing around with the delays didn't help.
Which delays did you modify? Did you try to increase I2C_WAIT/I2C_TIMEOUT?
I tried to increase both I2C_WAIT and I2C_TIMEOUT, and place my own
delays as well.
I was wondering if you might have some insights as to what may cause the
controller to behave this way other than unconfigured pads?
Unfortunately I don't have any hands-on experience with OMAP3 (apart from
some very quick testing on a AM3359 derivative), and cannot guarantee that
the I2C controller IP on OMAP3 is absolutely the same as on OMAP4/5 (most
probably it isn't; shall check this on Monday). Anyway, if everything else
is OK (muxmode/pad config, pull-ups, power, etc.), the only reasonable
explanation would be that there is not enough time for the controller to
update its status register under certain conditions, and these would be
either a slower clock rate (that makes byte transmission time come close
to the timeout), or clock stretching by some slaves; btw, the latter
seems probable, judging from your words that this happens in the address
phase, when some devices could take longer to prepare for action, and they
do this by stretching the clock. That is why I'm asking if you tried to
increase I2C_TIMEOUT. Did you do any measurements on the bus to see if all
is OK and the clock rate is right, and if it gets stretched by some slaves?
I believe I found the cause of the problem. In the new version of the
driver the following line was added to the exit sequence of i2c_write:
writew(0, i2c_base-cnt);
Removing this line solved the problem (module has been doing I2C
transactions for the last 16 hours or so without failing), and I
believe the reason has to do with Advisory 1.2 in the DM3730 errata:
Advisory 1.2I2C Module Does Not Allow 0-Byte Data Requests
Revision(s) Affected1.2, 1.1 and 1.0
Details When configured as the master, the I2C module
does not allow 0-byte data transfers.
Programming I2Ci.I2C_CNT[15:0]: DCOUNT = 0 will
cause undefined behavior.
Workaround(s) There is no workaround for this issue. Do not
use 0-byte data requests.
While the mentioned write is done at the end of i2c_write, perhaps the
driver's MO still triggers this issue. It certainly is plausible
that this line was missing from the old i2c_write exit sequence on
purpose, and not by accident (i2c_read, i2c_probe, and i2c_init all
had it in the old driver).
Regards,
Lubo
--
Regards,
Nikita.
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Re: [U-Boot] A question about unconfigured pads check in omap24xx_i2c
Hi Nikita,
On 11-Nov-13 13:15, Nikita Kiryanov wrote:
On 11/08/2013 11:26 PM, Lubomir Popov wrote:
Hi Nikita,
On 11/06/2013 03:19 PM, Lubomir Popov wrote:
On 06-Nov-13 14:12, Nikita Kiryanov wrote:
In drivers/i2c/omap24xx_i2c.c there are a few checks that attempt to
detect unconfigured pads for the i2c bus in use. These checks are
all in the form of
if (status == I2C_STAT_XRDY) {
printf(unconfigured pads\n);
return -1;
}
This check seems peculiar to me since the meaning of I2C_STAT_XRDY is
that new data is requested for transmission. Why is that
indication that
the bus is not padconf'd for I2C?
Hi Nikita,
This has been empirically confirmed on OMAP4 and OMAP5. When the pads
are not
configured, the I2C controller is actually disconnected from the bus.
The clock
input for its state machine has to come from the bus however due to
stretching
etc., although it is internally generated. So actually nothing changes
within
the controller after a transaction attempt is made, and it keeps its
initial
state with XRDY set only (ready to accept transmit data). I use
this as an
indicator. Not perfect, but works in most cases.
Regards,
Lubo
Thanks for the quick reply.
The reason I stumbled across this is that this check hasn't been
working
well on our OMAP3 based devices. Some I2C transactions work fine, but
some of them fail this check in the address phase, especially if the
I2C
transactions happen in quick successions.
You mean that you occasionally get this error on an otherwise properly
configured and working bus, right?
Yes.
Does this happen with particular
slave devices only, or randomly? And is it happening in the SPL, or in
regular U-Boot?
It happens in U-Boot when communicating with the PMIC (TPS65930),
but like I said, it worked in the driver's previous version, on the
same module.
We did not have any I2C issues
with the previous driver, and while this behavior is symptomatic of
timing issues playing around with the delays didn't help.
Which delays did you modify? Did you try to increase
I2C_WAIT/I2C_TIMEOUT?
I tried to increase both I2C_WAIT and I2C_TIMEOUT, and place my own
delays as well.
I was wondering if you might have some insights as to what may cause
the
controller to behave this way other than unconfigured pads?
Unfortunately I don't have any hands-on experience with OMAP3 (apart
from
some very quick testing on a AM3359 derivative), and cannot guarantee
that
the I2C controller IP on OMAP3 is absolutely the same as on OMAP4/5
(most
probably it isn't; shall check this on Monday). Anyway, if everything
else
is OK (muxmode/pad config, pull-ups, power, etc.), the only reasonable
explanation would be that there is not enough time for the controller to
update its status register under certain conditions, and these would be
either a slower clock rate (that makes byte transmission time come close
to the timeout), or clock stretching by some slaves; btw, the latter
seems probable, judging from your words that this happens in the address
phase, when some devices could take longer to prepare for action, and
they
do this by stretching the clock. That is why I'm asking if you tried to
increase I2C_TIMEOUT. Did you do any measurements on the bus to see
if all
is OK and the clock rate is right, and if it gets stretched by some
slaves?
I believe I found the cause of the problem. In the new version of the
driver the following line was added to the exit sequence of i2c_write:
writew(0, i2c_base-cnt);
Removing this line solved the problem (module has been doing I2C
transactions for the last 16 hours or so without failing), and I
believe the reason has to do with Advisory 1.2 in the DM3730 errata:
Advisory 1.2I2C Module Does Not Allow 0-Byte Data Requests
Revision(s) Affected1.2, 1.1 and 1.0
DetailsWhen configured as the master, the I2C module
does not allow 0-byte data transfers.
Programming I2Ci.I2C_CNT[15:0]: DCOUNT = 0 will
cause undefined behavior.
Workaround(s)There is no workaround for this issue. Do not
use 0-byte data requests.
While the mentioned write is done at the end of i2c_write, perhaps the
driver's MO still triggers this issue. It certainly is plausible
that this line was missing from the old i2c_write exit sequence on
purpose, and not by accident (i2c_read, i2c_probe, and i2c_init all
had it in the old driver).
Many thanks for catching this. Feel free to post a patch.
Lubo
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Re: [U-Boot] A question about unconfigured pads check in omap24xx_i2c
On 11/06/2013 03:19 PM, Lubomir Popov wrote:
On 06-Nov-13 14:12, Nikita Kiryanov wrote:
In drivers/i2c/omap24xx_i2c.c there are a few checks that attempt to
detect unconfigured pads for the i2c bus in use. These checks are
all in the form of
if (status == I2C_STAT_XRDY) {
printf(unconfigured pads\n);
return -1;
}
This check seems peculiar to me since the meaning of I2C_STAT_XRDY is
that new data is requested for transmission. Why is that indication that
the bus is not padconf'd for I2C?
Hi Nikita,
This has been empirically confirmed on OMAP4 and OMAP5. When the pads
are not
configured, the I2C controller is actually disconnected from the bus.
The clock
input for its state machine has to come from the bus however due to
stretching
etc., although it is internally generated. So actually nothing changes
within
the controller after a transaction attempt is made, and it keeps its
initial
state with XRDY set only (ready to accept transmit data). I use this as an
indicator. Not perfect, but works in most cases.
Regards,
Lubo
Thanks for the quick reply.
The reason I stumbled across this is that this check hasn't been working
well on our OMAP3 based devices. Some I2C transactions work fine, but
some of them fail this check in the address phase, especially if the I2C
transactions happen in quick successions. We did not have any I2C issues
with the previous driver, and while this behavior is symptomatic of
timing issues playing around with the delays didn't help.
I was wondering if you might have some insights as to what may cause the
controller to behave this way other than unconfigured pads?
--
Regards,
Nikita.
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Re: [U-Boot] A question about unconfigured pads check in omap24xx_i2c
Hi Nikita,
On 11/06/2013 03:19 PM, Lubomir Popov wrote:
On 06-Nov-13 14:12, Nikita Kiryanov wrote:
In drivers/i2c/omap24xx_i2c.c there are a few checks that attempt to
detect unconfigured pads for the i2c bus in use. These checks are
all in the form of
if (status == I2C_STAT_XRDY) {
printf(unconfigured pads\n);
return -1;
}
This check seems peculiar to me since the meaning of I2C_STAT_XRDY is
that new data is requested for transmission. Why is that indication that
the bus is not padconf'd for I2C?
Hi Nikita,
This has been empirically confirmed on OMAP4 and OMAP5. When the pads
are not
configured, the I2C controller is actually disconnected from the bus.
The clock
input for its state machine has to come from the bus however due to
stretching
etc., although it is internally generated. So actually nothing changes
within
the controller after a transaction attempt is made, and it keeps its
initial
state with XRDY set only (ready to accept transmit data). I use this as an
indicator. Not perfect, but works in most cases.
Regards,
Lubo
Thanks for the quick reply.
The reason I stumbled across this is that this check hasn't been working
well on our OMAP3 based devices. Some I2C transactions work fine, but
some of them fail this check in the address phase, especially if the I2C
transactions happen in quick successions.
You mean that you occasionally get this error on an otherwise properly
configured and working bus, right? Does this happen with particular
slave devices only, or randomly? And is it happening in the SPL, or in
regular U-Boot?
We did not have any I2C issues
with the previous driver, and while this behavior is symptomatic of
timing issues playing around with the delays didn't help.
Which delays did you modify? Did you try to increase I2C_WAIT/I2C_TIMEOUT?
I was wondering if you might have some insights as to what may cause the
controller to behave this way other than unconfigured pads?
Unfortunately I don't have any hands-on experience with OMAP3 (apart from
some very quick testing on a AM3359 derivative), and cannot guarantee that
the I2C controller IP on OMAP3 is absolutely the same as on OMAP4/5 (most
probably it isn't; shall check this on Monday). Anyway, if everything else
is OK (muxmode/pad config, pull-ups, power, etc.), the only reasonable
explanation would be that there is not enough time for the controller to
update its status register under certain conditions, and these would be
either a slower clock rate (that makes byte transmission time come close
to the timeout), or clock stretching by some slaves; btw, the latter
seems probable, judging from your words that this happens in the address
phase, when some devices could take longer to prepare for action, and they
do this by stretching the clock. That is why I'm asking if you tried to
increase I2C_TIMEOUT. Did you do any measurements on the bus to see if all
is OK and the clock rate is right, and if it gets stretched by some slaves?
Regards,
Lubo
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Re: [U-Boot] A question about unconfigured pads check in omap24xx_i2c
Hello Lubomir,
Am 07.11.2013 08:57, schrieb Lubomir Popov:
Hi Heiko,
On 07-Nov-13 7:14, Heiko Schocher wrote:
Hello Lubomir,
Am 06.11.2013 14:19, schrieb Lubomir Popov:
On 06-Nov-13 14:12, Nikita Kiryanov wrote:
In drivers/i2c/omap24xx_i2c.c there are a few checks that attempt to
detect unconfigured pads for the i2c bus in use. These checks are
all in the form of
if (status == I2C_STAT_XRDY) {
printf(unconfigured pads\n);
return -1;
}
This check seems peculiar to me since the meaning of I2C_STAT_XRDY is
that new data is requested for transmission. Why is that indication that
the bus is not padconf'd for I2C?
Hi Nikita,
This has been empirically confirmed on OMAP4 and OMAP5. When the pads are not
configured, the I2C controller is actually disconnected from the bus. The clock
input for its state machine has to come from the bus however due to stretching
etc., although it is internally generated. So actually nothing changes within
the controller after a transaction attempt is made, and it keeps its initial
state with XRDY set only (ready to accept transmit data). I use this as an
indicator. Not perfect, but works in most cases.
Thanks for this explanation! Maybe we can document this somewhere in
the code?
bye,
Heiko
You are right, it would be good to document it. Unfortunately I have not
been on the U-Boot wave for some months now due to very heavy engagement
with other stuff; have even unsubscribed from the list. I think however
that in order to give definite statements and improve the driver, a new
round of experiments has to be made to cover the two major types of design
flaws (software and/or hardware): incorrect pad configuration, and missing
pullups (internal or external). I wrote this driver more that 6 months ago
with the goal to have something working properly (the then existing one was,
mildly put, not good), and this detection is just a bonus side effect.
In summary, the professional approach would require some more effort, which
I'm not sure when I could afford. Otherwise, if just an explanation for the
current algo is to be given, no problem - I can just add some comments.
I vote for the professional approach ;-) But if you have no time, and
can just send a comment for the current state (maybe with a short summary,
what should be done) I am fine with this too!
Thanks!
bye,
Heiko
--
DENX Software Engineering GmbH, MD: Wolfgang Denk Detlev Zundel
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
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Re: [U-Boot] A question about unconfigured pads check in omap24xx_i2c
Heiko,
On 07-Nov-13 10:04, Heiko Schocher wrote:
Hello Lubomir,
Am 07.11.2013 08:57, schrieb Lubomir Popov:
Hi Heiko,
On 07-Nov-13 7:14, Heiko Schocher wrote:
Hello Lubomir,
Am 06.11.2013 14:19, schrieb Lubomir Popov:
On 06-Nov-13 14:12, Nikita Kiryanov wrote:
In drivers/i2c/omap24xx_i2c.c there are a few checks that attempt to
detect unconfigured pads for the i2c bus in use. These checks are
all in the form of
if (status == I2C_STAT_XRDY) {
printf(unconfigured pads\n);
return -1;
}
This check seems peculiar to me since the meaning of I2C_STAT_XRDY is
that new data is requested for transmission. Why is that
indication that
the bus is not padconf'd for I2C?
Hi Nikita,
This has been empirically confirmed on OMAP4 and OMAP5. When the
pads are not
configured, the I2C controller is actually disconnected from the
bus. The clock
input for its state machine has to come from the bus however due to
stretching
etc., although it is internally generated. So actually nothing
changes within
the controller after a transaction attempt is made, and it keeps
its initial
state with XRDY set only (ready to accept transmit data). I use
this as an
indicator. Not perfect, but works in most cases.
Thanks for this explanation! Maybe we can document this somewhere in
the code?
bye,
Heiko
You are right, it would be good to document it. Unfortunately I have not
been on the U-Boot wave for some months now due to very heavy engagement
with other stuff; have even unsubscribed from the list. I think however
that in order to give definite statements and improve the driver, a new
round of experiments has to be made to cover the two major types of
design
flaws (software and/or hardware): incorrect pad configuration, and
missing
pullups (internal or external). I wrote this driver more that 6
months ago
with the goal to have something working properly (the then existing
one was,
mildly put, not good), and this detection is just a bonus side effect.
In summary, the professional approach would require some more effort,
which
I'm not sure when I could afford. Otherwise, if just an explanation
for the
current algo is to be given, no problem - I can just add some comments.
I vote for the professional approach ;-) But if you have no time, and
can just send a comment for the current state (maybe with a short
summary,
what should be done) I am fine with this too!
OK, shall see to the easy way first - just add some comments, sometime
next week.
But, no promises ;-)
Lubo
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Re: [U-Boot] A question about unconfigured pads check in omap24xx_i2c
On 06-Nov-13 14:12, Nikita Kiryanov wrote:
In drivers/i2c/omap24xx_i2c.c there are a few checks that attempt to
detect unconfigured pads for the i2c bus in use. These checks are
all in the form of
if (status == I2C_STAT_XRDY) {
printf(unconfigured pads\n);
return -1;
}
This check seems peculiar to me since the meaning of I2C_STAT_XRDY is
that new data is requested for transmission. Why is that indication that
the bus is not padconf'd for I2C?
Hi Nikita,
This has been empirically confirmed on OMAP4 and OMAP5. When the pads
are not
configured, the I2C controller is actually disconnected from the bus.
The clock
input for its state machine has to come from the bus however due to
stretching
etc., although it is internally generated. So actually nothing changes
within
the controller after a transaction attempt is made, and it keeps its initial
state with XRDY set only (ready to accept transmit data). I use this as an
indicator. Not perfect, but works in most cases.
Regards,
Lubo
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Re: [U-Boot] A question about unconfigured pads check in omap24xx_i2c
Hello Lubomir,
Am 06.11.2013 14:19, schrieb Lubomir Popov:
On 06-Nov-13 14:12, Nikita Kiryanov wrote:
In drivers/i2c/omap24xx_i2c.c there are a few checks that attempt to
detect unconfigured pads for the i2c bus in use. These checks are
all in the form of
if (status == I2C_STAT_XRDY) {
printf(unconfigured pads\n);
return -1;
}
This check seems peculiar to me since the meaning of I2C_STAT_XRDY is
that new data is requested for transmission. Why is that indication that
the bus is not padconf'd for I2C?
Hi Nikita,
This has been empirically confirmed on OMAP4 and OMAP5. When the pads are not
configured, the I2C controller is actually disconnected from the bus. The clock
input for its state machine has to come from the bus however due to stretching
etc., although it is internally generated. So actually nothing changes within
the controller after a transaction attempt is made, and it keeps its initial
state with XRDY set only (ready to accept transmit data). I use this as an
indicator. Not perfect, but works in most cases.
Thanks for this explanation! Maybe we can document this somewhere in
the code?
bye,
Heiko
--
DENX Software Engineering GmbH, MD: Wolfgang Denk Detlev Zundel
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
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Re: [U-Boot] A question about unconfigured pads check in omap24xx_i2c
Hi Heiko,
On 07-Nov-13 7:14, Heiko Schocher wrote:
Hello Lubomir,
Am 06.11.2013 14:19, schrieb Lubomir Popov:
On 06-Nov-13 14:12, Nikita Kiryanov wrote:
In drivers/i2c/omap24xx_i2c.c there are a few checks that attempt to
detect unconfigured pads for the i2c bus in use. These checks are
all in the form of
if (status == I2C_STAT_XRDY) {
printf(unconfigured pads\n);
return -1;
}
This check seems peculiar to me since the meaning of I2C_STAT_XRDY is
that new data is requested for transmission. Why is that indication
that
the bus is not padconf'd for I2C?
Hi Nikita,
This has been empirically confirmed on OMAP4 and OMAP5. When the pads
are not
configured, the I2C controller is actually disconnected from the bus.
The clock
input for its state machine has to come from the bus however due to
stretching
etc., although it is internally generated. So actually nothing
changes within
the controller after a transaction attempt is made, and it keeps its
initial
state with XRDY set only (ready to accept transmit data). I use this
as an
indicator. Not perfect, but works in most cases.
Thanks for this explanation! Maybe we can document this somewhere in
the code?
bye,
Heiko
You are right, it would be good to document it. Unfortunately I have not
been on the U-Boot wave for some months now due to very heavy engagement
with other stuff; have even unsubscribed from the list. I think however
that in order to give definite statements and improve the driver, a new
round of experiments has to be made to cover the two major types of design
flaws (software and/or hardware): incorrect pad configuration, and missing
pullups (internal or external). I wrote this driver more that 6 months ago
with the goal to have something working properly (the then existing one was,
mildly put, not good), and this detection is just a bonus side effect.
In summary, the professional approach would require some more effort, which
I'm not sure when I could afford. Otherwise, if just an explanation for the
current algo is to be given, no problem - I can just add some comments.
What do you think?
Regards,
Lubo
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