Re: [PATCH v2 07/11] drm/dp: Add drm_dp_uhbr_channel_coding_supported()

[Imre Deak <imre.deak@intel.com>]

On Wed, Apr 17, 2024 at 12:21:58PM +0300, Jani Nikula wrote:
> On Wed, 17 Apr 2024, Imre Deak <imre.deak@intel.com> wrote:
> > Factor out a function to check for UHBR channel coding support used by a
> > follow-up patch in the patchset.
> >
> > Cc: dri-devel@lists.freedesktop.org
> > Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
> > Reviewed-by: Manasi Navare <navaremanasi@chromium.org>
> > Acked-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> > Signed-off-by: Imre Deak <imre.deak@intel.com>
> > ---
> >  drivers/gpu/drm/i915/display/intel_dp.c | 2 +-
> >  include/drm/display/drm_dp_helper.h     | 6 ++++++
> >  2 files changed, 7 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> > index 23808e9d41d5d..41127069b55e4 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> > @@ -225,7 +225,7 @@ static void intel_dp_set_dpcd_sink_rates(struct intel_dp *intel_dp)
> >  	 * Sink rates for 128b/132b. If set, sink should support all 8b/10b
> >  	 * rates and 10 Gbps.
> >  	 */
> > -	if (intel_dp->dpcd[DP_MAIN_LINK_CHANNEL_CODING] & DP_CAP_ANSI_128B132B) {
> > +	if (drm_dp_uhbr_channel_coding_supported(intel_dp->dpcd)) {
> >  		u8 uhbr_rates = 0;
> >  
> >  		BUILD_BUG_ON(ARRAY_SIZE(intel_dp->sink_rates) < ARRAY_SIZE(dp_rates) + 3);
> > diff --git a/include/drm/display/drm_dp_helper.h b/include/drm/display/drm_dp_helper.h
> > index baf9949ff96fc..8a64fe8d97af2 100644
> > --- a/include/drm/display/drm_dp_helper.h
> > +++ b/include/drm/display/drm_dp_helper.h
> > @@ -251,6 +251,12 @@ drm_dp_channel_coding_supported(const u8 dpcd[DP_RECEIVER_CAP_SIZE])
> >  	return dpcd[DP_MAIN_LINK_CHANNEL_CODING] & DP_CAP_ANSI_8B10B;
> >  }
> >  
> > +static inline bool
> > +drm_dp_uhbr_channel_coding_supported(const u8 dpcd[DP_RECEIVER_CAP_SIZE])
> > +{
> > +	return dpcd[DP_MAIN_LINK_CHANNEL_CODING] & DP_CAP_ANSI_128B132B;
> > +}
> 
> Nitpick, "uhbr channel coding" is not pedantically correct, and it does
> rub me the wrong way.
> 
> Yes, using 128b/132b channel coding implies UHBR, and UHBR requires
> 128b/132b channel coding, but they are not the same thing. We do
> conflate the two quite a bit in the code, checking for UHBR when we
> really mean 128b/132b, but embedding this confusion in the function name
> directly is a bit much.
> 
> I've named the link training functions drm_dp_128b132b_* in the same
> file, and I think this one should be named similarly. Maybe just
> drm_dp_128b132b_supported(), and rename
> drm_dp_channel_coding_supported() to drm_dp_8b10b_supported() to unify?

Ok, makes sense, will rename it to drm_dp_128b132b_supported() and
can do the same - as a follow-up - for 8b10b.

> BR,
> Jani.
> 
> 
> 
> > +
> >  static inline bool
> >  drm_dp_alternate_scrambler_reset_cap(const u8 dpcd[DP_RECEIVER_CAP_SIZE])
> >  {
> 
> -- 
> Jani Nikula, Intel