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

["Uwe Kleine-König" <u.kleine-koenig-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>]

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.

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.

Best regards
Uwe

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Pengutronix e.K.                           | Uwe Kleine-König            |
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