Re: [PATCH] i2c: i2c_mxs: Set ACK_MODE bit

[Marek Vasut <marex-ynQEQJNshbs@public.gmane.org>]

Dear Uwe Kleine-König,

> Hello,
> 
> On Mon, Aug 19, 2013 at 09:19:01AM -0300, Fabio Estevam wrote:
> > On 08/15/2013 07:08 AM, Wolfram Sang wrote:
> > >On Tue, Jul 02, 2013 at 01:01:00PM -0300, Fabio Estevam wrote:
> > >>According to mx23 erratum 2727:
> > >>
> > >>"2727 : I2C 9th Clock Pulse (ACK) not generated when RETAIN_CLOCK set.
> > >>
> > >>Description:
> > >>
> > >>When RETAIN_CLOCK is set, the ninth clock pulse (ACK) is not generated.
> > >>However, the SDA line is read at the proper timing interval. If
> > >>RETAIN_CLOCK is cleared, the ninth clock pulse is generated.
> > >>Also, the HW_I2C_VERSION register incorrectly states the version is
> > >>1.2. It should be 1.3.
> > >>
> > >>Workaround:
> > >>HW_I2C_CTRL1[ACK_MODE] has default value of 0. It should be set to 1 to
> > >>enable the fix for this issue."
> > >>
> > >>It has also been noticed that mx28 needs to implement this fix in order
> > >>to have SMBus to work properly.
> > >>
> > >>Reported-by: Christoph Baumann <cb-/RsSufbtIHM@public.gmane.org>
> > >>Signed-off-by: Fabio Estevam <fabio.estevam-KZfg59tc24xl57MIdRCFDg@public.gmane.org>
> > >
> > >What's with this one? Bogus? Needed? Still needed after PIO rework?
> > 
> > According to the mx23 erratum 2727 this patch is needed.
> 
> Last time I worked with i2c stuff on mxs my impression was the mx23
> erratum 2727 is non-sense. Having HW_I2C_CTRL1[ACK_MODE] set or not
> didn't made any difference in my tests.

Yeah, I can confirm this one.

> I suspect that the description isn't complete. So the driver does
> already use RETAIN_CLOCK (for the select phase) which up to know didn't
> made any problems on mx23 even without having ACK_MODE=1.
> 
> The statement about the HW_I2C_VERSION register appears just misplaced
> there.
> 
> So I'd vote for not taking this patch until there is a better
> understanding of the eventual problem.

I was doing some pretty thorough test when doing the PIO rework and watched the 
bus with LA, but didn't notice any difference whether the bit was or wasnt set. 
So either way WFM. On MX28 though, the bit is set after the I2C block is reset, 
on MX23 it is unset, that's the only thing I observed.

Best regards,
Marek Vasut