Re: [Intel-gfx] [PATCH 1/3] drm/i915: Try to use fast+narrow link on eDP again and fall back to the old max strategy on failure

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Thu, Mar 19, 2020 at 03:20:50PM -0700, Manasi Navare wrote:
> On Thu, Mar 19, 2020 at 06:38:42PM +0200, Ville Syrjala wrote:
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > 
> > Some new eDP panels don't like to operate at the max parameters, and
> > instead we need to go for an optimal confiugration. That unfortunately
> > doesn't work with older eDP panels which are generally only guaranteed
> > to work at the max parameters.
> > 
> > To solve these two conflicting requirements let's start with the optimal
> > setup, and if that fails we start again with the max parameters. The
> > downside is probably an extra modeset when we switch strategies but
> > I don't see a good way to avoid that.
> > 
> > For a bit of history we first tried to go for the fast+narrow in
> > commit 7769db588384 ("drm/i915/dp: optimize eDP 1.4+ link config
> > fast and narrow"). but that had to be reverted due to regression
> > on older panels in commit f11cb1c19ad0 ("drm/i915/dp: revert back
> > to max link rate and lane count on eDP"). So now we try to get
> > the best of both worlds by using both strategies.
> > 
> > v2: Deal with output_bpp and uapi vs. hw state split
> >     Reword some comments
> > 
> > Cc: Jani Nikula <jani.nikula@intel.com>
> > Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
> > Cc: Manasi Navare <manasi.d.navare@intel.com>
> > Cc: Albert Astals Cid <aacid@kde.org> # v5.0 backport
> > Cc: Emanuele Panigati <ilpanich@gmail.com> # v5.0 backport
> > Cc: Matteo Iervasi <matteoiervasi@gmail.com> # v5.0 backport
> > Cc: Timo Aaltonen <tjaalton@ubuntu.com>
> > References: https://bugs.freedesktop.org/show_bug.cgi?id=105267
> > References: https://bugs.freedesktop.org/show_bug.cgi?id=109959
> > References: https://gitlab.freedesktop.org/drm/intel/issues/272
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> This approach looks good to me to fallback to max parameters if
> it fails the first time.
> 
> > ---
> >  .../drm/i915/display/intel_display_types.h    |  1 +
> >  drivers/gpu/drm/i915/display/intel_dp.c       | 74 ++++++++++++++++---
> >  2 files changed, 66 insertions(+), 9 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h b/drivers/gpu/drm/i915/display/intel_display_types.h
> > index 5e00e611f077..ffde0d4af23c 100644
> > --- a/drivers/gpu/drm/i915/display/intel_display_types.h
> > +++ b/drivers/gpu/drm/i915/display/intel_display_types.h
> > @@ -1258,6 +1258,7 @@ struct intel_dp {
> >  	bool link_trained;
> >  	bool has_audio;
> >  	bool reset_link_params;
> > +	bool use_max_params;
> >  	u8 dpcd[DP_RECEIVER_CAP_SIZE];
> >  	u8 psr_dpcd[EDP_PSR_RECEIVER_CAP_SIZE];
> >  	u8 downstream_ports[DP_MAX_DOWNSTREAM_PORTS];
> > diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> > index ef2e06e292d5..85abcce492ca 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> > @@ -465,6 +465,12 @@ int intel_dp_get_link_train_fallback_values(struct intel_dp *intel_dp,
> >  {
> >  	int index;
> >  
> > +	if (intel_dp_is_edp(intel_dp) && !intel_dp->use_max_params) {
> > +		DRM_DEBUG_KMS("Retrying Link training for eDP with max parameters\n");
> > +		intel_dp->use_max_params = true;
> > +		return 0;
> > +	}
> 
> We need to remove the current check for intel_dp_can_link_train_fallback_for_edp() right?

No. Why do you think it needs to be removed?

-- 
Ville Syrjälä
Intel
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