Re: [PATCH 4/4] I2C: OMAP3: PM: (re)init for every transfer to support off-mode

[Kevin Hilman <khilman@deeprootsystems.com>]

"Hunter, Jon" <jon-hunter@ti.com> writes:

> Hi Kevin,
>
>> Shouldn't you do a read-modify-write of I2C_CON_REG here?  Otherwise,
>> you're loosing any of the other settings in I2C_CON_REG.
>>
>> Not being an expert in the I2C hardware, I'm not sure if it matters,
>> but this doesn't seem quite right due to possible side effects.
>
> This is a good question and this exact same issue came up on the
> omapzoom tree. For the omapzoom tree we ended up not implementing a
> read-modify-write here. The reason being that omap_i2c_unidle is
> called at the beginning of every transfer and we are re-configuring
> the I2C_CON register for every transfer. So when consulting with the
> TI linux team they said that it is ok to simply write 0 and clear
> the register here so we start over fresh for each transfer.
>
> I was trying to think if there would be any harm in doing a
> read-modify-write here. Probably not. You would not want the STT bit
> (generate a start command) to get set, however, this bit should not
> be set in the first place when entering this function.
>
> This change has been implemented in the omapzoom tree and so for you
>reference please see:
>http://git.omapzoom.org/?p=repo/omapkernel.git;a=commit;h=ec70a0af52df54638a4fa33fc0dc3d24b1f893f1

Jon, thanks for the clarification.  I will fold this change into
the upstream-bound I2C changes.

Also thanks for the pointer to the original patch with author/signoff
credits.

Tao, in the future please be sure to cite original authors and/or
sources when submitting patches to the list.

Thanks,

Kevin