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

[Rodrigo Vivi <rodrigo.vivi@intel.com>]

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.
> 
> 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>

I can hear from here your "I told you so"... Sorry!

Reviewed-by: Rodrigo Vivi <rodrigo.vivi@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
>