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
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