From mboxrd@z Thu Jan 1 00:00:00 1970 From: vaibhav.hiremath@linaro.org (Vaibhav Hiremath) Date: Sat, 30 May 2015 01:50:12 +0530 Subject: [PATCH 03/12] i2c: pxa: Add reset operation when i2c bus busy In-Reply-To: <878uc7yxzx.fsf@belgarion.home> References: <1432818224-17070-1-git-send-email-vaibhav.hiremath@linaro.org> <1432818224-17070-4-git-send-email-vaibhav.hiremath@linaro.org> <878uc7yxzx.fsf@belgarion.home> Message-ID: <5568C9FC.7040906@linaro.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Saturday 30 May 2015 01:09 AM, Robert Jarzmik wrote: > Vaibhav Hiremath writes: > >> From: "Jett.Zhou" >> >> According to some test in emei_dkb, we found some i2c slave device >> (eg. camera sensor ov2659 power up) introduce noise on sda, so detect >> i2c controller busy, and assert reset to i2c controller to recover as >> early as possible to avoid more latency on the entire i2c transaction. >> >> Signed-off-by: Jett.Zhou >> [vaibhav.hiremath at linaro.org: Removed reduction in timeout value, as I >> do not have goot explanation for it. Logically it is not required. >> And also Updated changelog] >> Signed-off-by: Vaibhav Hiremath >> >> Signed-off-by: Vaibhav Hiremath >> --- >> drivers/i2c/busses/i2c-pxa.c | 4 ++++ >> 1 file changed, 4 insertions(+) >> >> diff --git a/drivers/i2c/busses/i2c-pxa.c b/drivers/i2c/busses/i2c-pxa.c >> index d4c798a..a76c901 100644 >> --- a/drivers/i2c/busses/i2c-pxa.c >> +++ b/drivers/i2c/busses/i2c-pxa.c >> @@ -314,6 +314,10 @@ static int i2c_pxa_wait_bus_not_busy(struct pxa_i2c *i2c) >> { >> int timeout = DEF_TIMEOUT; >> >> + if (readl(_ISR(i2c)) & (ISR_IBB | ISR_UB)) >> + i2c_pxa_reset(i2c); > > The pxa27x manual states in the Developer Manual, chapter 9.4.13 "Reset > Conditions" : > Software must ensure that (1) the I 2 C unit is not busy before it > asserts a reset > > Given that, I don't agree with this patch. Hmmm, Just saw pxa27x manual, and you are right. In that case I am not sure how to address the issue mentioned in the changelog. On the other side, Check for ISR_IBB, should be ok, as, as per spec it says, "Set when the TWSI bus is busy but the SoC TWSI is not involved in the transaction." Also, I believe we should be ok, as the first thing we do in i2c_pxa_reset() is abort the current transaction and then assert reset. Isn't it? > Moreover, reseting unconditionaly the > i2c bus on each busy state on a write transaction for one single corner case is > not something that has my agreement. A quirk might overcome my reluctance. > Any condition check you can possibly think of for asserting reset??? Having said that, Somewhere I do agree with you that we need to further debug on noise issue in HW rather hacking software. :) I am ok to drop this patch, do further testing and revisit again if issue persist. Thanks, Vaibhav