Re: [PATCH 4/8 v7] drm/i915/intel_i2c: use WAIT cycle, not STOP

Daniel Kurtz
2012-04-10T10:56:37Z

On Tue, Apr 10, 2012 at 6:41 PM, Daniel Vetter <daniel@ffwll.ch> wrote:
> On Tue, Apr 10, 2012 at 12:37:46PM +0200, Daniel Vetter wrote:
>> On Fri, Mar 30, 2012 at 07:46:39PM +0800, Daniel Kurtz wrote:
>> > The i915 is only able to generate a STOP cycle (i.e. finalize an i2c
>> > transaction) during a DATA or WAIT phase.  In other words, the
>> > controller rejects a STOP requested as part of the first transaction in a
>> > sequence.
>> >
>> > Thus, for the first transaction we must always use a WAIT cycle, detect
>> > when the device has finished (and is in a WAIT phase), and then either
>> > start the next transaction, or, if there are no more transactions,
>> > generate a STOP cycle.
>> >
>> > Note: Theoretically, the last transaction of a multi-transaction sequence
>> > could initiate a STOP cycle.  However, this slight optimization is left
>> > for another patch.  We return -ETIMEDOUT if the hardware doesn't
>> > deactivate after the STOP cycle.
>> >
>> > Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>
>>
>> I've re-read gmbus register spec and STOP seems to be allowed even in the
>> first cycle. Does this patch solve an issue for you? If not, I prefer we
>> just drop it.

STOP does not work in the first cycle, hence the patch.

-Daniel

>
> Actually I'd like to keep the -ETIMEDOUT return value, so maybe we should
> keeep that hunk. I've picked up the previous 3 patches of this series, the
> once after this one here conflict (without this patch here).
> -Daniel
> --
> Daniel Vetter
> Mail: daniel@ffwll.ch
> Mobile: +41 (0)79 365 57 48