Re: [PATCH v2] drm/i915/dp: revert back to max link rate and lane count on eDP

[Manasi Navare <manasi.d.navare@intel.com>]

On Fri, Apr 05, 2019 at 01:13:11PM -0700, Rodrigo Vivi wrote:
> On Fri, Apr 05, 2019 at 11:18:25AM -0700, Manasi Navare wrote:
> > On Fri, Apr 05, 2019 at 10:52:20AM +0300, Jani Nikula wrote:
> > > Commit 7769db588384 ("drm/i915/dp: optimize eDP 1.4+ link config fast
> > > and narrow") started to optize the eDP 1.4+ link config, both per spec
> > > and as preparation for display stream compression support.
> > > 
> > > Sadly, we again face panels that flat out fail with parameters they
> > > claim to support. Revert, and go back to the drawing board.
> > 
> > Yup, already multiple users facing this issue with eDP 1.4 panels that require
> > max parameters to pass link train.
> 
> I was wondering if we should blacklist the panel/platform, but if
> there are multiple cases it is better to revert...

Yes the bug has been reported and seen by atleast 4 users on different eDP panel product IDs

> 
> Unless there's a way to try and fallback quickly?!

I submitted a patch earlier to fallback with max parameters if optimized ones dont work:
https://patchwork.freedesktop.org/patch/296273/?series=58975&rev=2

But airlied suugested a revert instead.

Manasi

> 
> > 
> > I hear you now :)
> > 
> > Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
> > 
> > > 
> > > v2: Actually revert to max params instead of just wide-and-slow.
> > > 
> > > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=109959
> > > Fixes: 7769db588384 ("drm/i915/dp: optimize eDP 1.4+ link config fast and narrow")
> > > Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > > Cc: Manasi Navare <manasi.d.navare@intel.com>
> > > Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
> > > Cc: Matt Atwood <matthew.s.atwood@intel.com>
> > > Cc: "Lee, Shawn C" <shawn.c.lee@intel.com>
> > > Cc: Dave Airlie <airlied@gmail.com>
> > > Cc: intel-gfx@lists.freedesktop.org
> > > Cc: <stable@vger.kernel.org> # v5.0+
> > > Signed-off-by: Jani Nikula <jani.nikula@intel.com>
> > > ---
> > >  drivers/gpu/drm/i915/intel_dp.c | 69 +++++----------------------------
> > >  1 file changed, 10 insertions(+), 59 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> > > index 72c490..dfa770 100644
> > > --- a/drivers/gpu/drm/i915/intel_dp.c
> > > +++ b/drivers/gpu/drm/i915/intel_dp.c
> > > @@ -1856,42 +1856,6 @@ intel_dp_compute_link_config_wide(struct intel_dp *intel_dp,
> > >  	return -EINVAL;
> > >  }
> > >  
> > > -/* Optimize link config in order: max bpp, min lanes, min clock */
> > > -static int
> > > -intel_dp_compute_link_config_fast(struct intel_dp *intel_dp,
> > > -				  struct intel_crtc_state *pipe_config,
> > > -				  const struct link_config_limits *limits)
> > > -{
> > > -	struct drm_display_mode *adjusted_mode = &pipe_config->base.adjusted_mode;
> > > -	int bpp, clock, lane_count;
> > > -	int mode_rate, link_clock, link_avail;
> > > -
> > > -	for (bpp = limits->max_bpp; bpp >= limits->min_bpp; bpp -= 2 * 3) {
> > > -		mode_rate = intel_dp_link_required(adjusted_mode->crtc_clock,
> > > -						   bpp);
> > > -
> > > -		for (lane_count = limits->min_lane_count;
> > > -		     lane_count <= limits->max_lane_count;
> > > -		     lane_count <<= 1) {
> > > -			for (clock = limits->min_clock; clock <= limits->max_clock; clock++) {
> > > -				link_clock = intel_dp->common_rates[clock];
> > > -				link_avail = intel_dp_max_data_rate(link_clock,
> > > -								    lane_count);
> > > -
> > > -				if (mode_rate <= link_avail) {
> > > -					pipe_config->lane_count = lane_count;
> > > -					pipe_config->pipe_bpp = bpp;
> > > -					pipe_config->port_clock = link_clock;
> > > -
> > > -					return 0;
> > > -				}
> > > -			}
> > > -		}
> > > -	}
> > > -
> > > -	return -EINVAL;
> > > -}
> > > -
> > >  static int intel_dp_dsc_compute_bpp(struct intel_dp *intel_dp, u8 dsc_max_bpc)
> > >  {
> > >  	int i, num_bpc;
> > > @@ -2028,15 +1992,13 @@ intel_dp_compute_link_config(struct intel_encoder *encoder,
> > >  	limits.min_bpp = 6 * 3;
> > >  	limits.max_bpp = intel_dp_compute_bpp(intel_dp, pipe_config);
> > >  
> > > -	if (intel_dp_is_edp(intel_dp) && intel_dp->edp_dpcd[0] < DP_EDP_14) {
> > > +	if (intel_dp_is_edp(intel_dp)) {
> > >  		/*
> > >  		 * Use the maximum clock and number of lanes the eDP panel
> > > -		 * advertizes being capable of. The eDP 1.3 and earlier panels
> > > -		 * are generally designed to support only a single clock and
> > > -		 * lane configuration, and typically these values correspond to
> > > -		 * the native resolution of the panel. With eDP 1.4 rate select
> > > -		 * and DSC, this is decreasingly the case, and we need to be
> > > -		 * able to select less than maximum link config.
> > > +		 * advertizes being capable of. The panels are generally
> > > +		 * designed to support only a single clock and lane
> > > +		 * configuration, and typically these values correspond to the
> > > +		 * native resolution of the panel.
> > >  		 */
> > >  		limits.min_lane_count = limits.max_lane_count;
> > >  		limits.min_clock = limits.max_clock;
> > > @@ -2050,22 +2012,11 @@ intel_dp_compute_link_config(struct intel_encoder *encoder,
> > >  		      intel_dp->common_rates[limits.max_clock],
> > >  		      limits.max_bpp, adjusted_mode->crtc_clock);
> > >  
> > > -	if (intel_dp_is_edp(intel_dp))
> > > -		/*
> > > -		 * Optimize for fast and narrow. eDP 1.3 section 3.3 and eDP 1.4
> > > -		 * section A.1: "It is recommended that the minimum number of
> > > -		 * lanes be used, using the minimum link rate allowed for that
> > > -		 * lane configuration."
> > > -		 *
> > > -		 * Note that we use the max clock and lane count for eDP 1.3 and
> > > -		 * earlier, and fast vs. wide is irrelevant.
> > > -		 */
> > > -		ret = intel_dp_compute_link_config_fast(intel_dp, pipe_config,
> > > -							&limits);
> > > -	else
> > > -		/* Optimize for slow and wide. */
> > > -		ret = intel_dp_compute_link_config_wide(intel_dp, pipe_config,
> > > -							&limits);
> > > +	/*
> > > +	 * Optimize for slow and wide. This is the place to add alternative
> > > +	 * optimization policy.
> > > +	 */
> > > +	ret = intel_dp_compute_link_config_wide(intel_dp, pipe_config, &limits);
> > >  
> > >  	/* enable compression if the mode doesn't fit available BW */
> > >  	DRM_DEBUG_KMS("Force DSC en = %d\n", intel_dp->force_dsc_en);
> > > -- 
> > > 2.20.1
> > >