[Intel-gfx] [PATCH 1/4] drm/i915/dp: retry i2c-over-aux seven times on AUX DEFER

[Todd Previte]

Yep. Good to go.

Reviewed-by: Todd Previte <tprevite at gmail.com>


On Fri, Sep 27, 2013 at 4:51 AM, Jani Nikula <jani.nikula at linux.intel.com>wrote:

> On Fri, 20 Sep 2013, Todd Previte <tprevite at gmail.com> wrote:
> > On 09/20/2013 06:42 AM, Jani Nikula wrote:
> >> Per DP1.2 spec.
> >>
> >> Signed-off-by: Jani Nikula <jani.nikula at intel.com>
> >> ---
> >>   drivers/gpu/drm/i915/intel_dp.c |    7 ++++++-
> >>   1 file changed, 6 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/gpu/drm/i915/intel_dp.c
> b/drivers/gpu/drm/i915/intel_dp.c
> >> index 9770160..6626514 100644
> >> --- a/drivers/gpu/drm/i915/intel_dp.c
> >> +++ b/drivers/gpu/drm/i915/intel_dp.c
> >> @@ -654,7 +654,12 @@ intel_dp_i2c_aux_ch(struct i2c_adapter *adapter,
> int mode,
> >>              break;
> >>      }
> >>
> >> -    for (retry = 0; retry < 5; retry++) {
> >> +    /*
> >> +     * DP1.2 sections 2.7.7.1.5.6.1 and 2.7.7.1.6.6.1: A DP Source
> device is
> >> +     * required to retry at least seven times upon receiving AUX_DEFER
> >> +     * before giving up the AUX transaction.
> >> +     */
> >> +    for (retry = 0; retry < 7; retry++) {
> >>              ret = intel_dp_aux_ch(intel_dp,
> >>                                    msg, msg_bytes,
> >>                                    reply, reply_bytes);
> >>
> > Hey Jani,
> >
> > Although it's not explicitly stated in the specification (I went through
> > both the 1.1a and 1.2a specifications and couldn't find it), I think the
> > the retry count of 7 applies to all AUX transactions, both native and
> > I2C. That's alluded to in the description of the link training sequence
> > (pg 382, 2nd paragraph from the bottom) where the sink may defer up to
> > seven times before the source can abort training.
> >
> > With that in mind, it might be a good idea to use a defined constant for
> > the retry count for both native and I2C AUX transactions. That would
> > keep it consistent throughout the code and be easier to update moving
> > forward should the specification change.
>
> Todd, are you willing to give your reviewed-by on this one patch per our
> irc discussion? We can do further cleanups later.
>
> I've sent a new version of 3/4 with the #defines separately.
>
>
> BR,
> Jani.
>
>
>
> --
> Jani Nikula, Intel Open Source Technology Center
>
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