[U-Boot] A question about unconfigured pads check in omap24xx_i2c
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?
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
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
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
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
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
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?
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
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 1.2 I2C Module Does Not Allow 0-Byte Data Requests Revision(s) Affected 1.2, 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
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 1.2 I2C Module Does Not Allow 0-Byte Data Requests Revision(s) Affected 1.2, 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).
Many thanks for catching this. Feel free to post a patch.
Lubo
participants (3)
-
Heiko Schocher -
Lubomir Popov -
Nikita Kiryanov