Re: [PATCH 6/7] drm/i915/dp: abstract link config selection

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

On Thu, Apr 05, 2018 at 05:39:04PM +0300, Jani Nikula wrote:
> For now, there's just the one link config selection, optimizing for slow
> and wide link. No functional changes.
> 
> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
> ---
>  drivers/gpu/drm/i915/intel_dp.c | 81 +++++++++++++++++++++++++----------------
>  1 file changed, 50 insertions(+), 31 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index 3c5fbdf42b9b..c98626b3af65 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -1704,6 +1704,42 @@ static bool intel_edp_compare_alt_mode(struct drm_display_mode *m1,
>  	return bres;
>  }
>  
> +/* Optimize link config in order: max bpp, min clock, min lanes */
> +static bool
> +intel_dp_compute_link_config_wide(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 (clock = limits->min_clock; clock <= limits->max_clock; clock++) {
> +			for (lane_count = limits->min_lane_count;
> +			     lane_count <= limits->max_lane_count;
> +			     lane_count <<= 1) {
> +				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 true;
> +				}
> +			}
> +		}
> +	}
> +
> +	return false;
> +}
> +
>  static bool
>  intel_dp_compute_link_config(struct intel_encoder *encoder,
>  			     struct intel_crtc_state *pipe_config)
> @@ -1711,8 +1747,6 @@ intel_dp_compute_link_config(struct intel_encoder *encoder,
>  	struct drm_display_mode *adjusted_mode = &pipe_config->base.adjusted_mode;
>  	struct intel_dp *intel_dp = enc_to_intel_dp(&encoder->base);
>  	struct link_config_limits limits;
> -	int bpp, clock, lane_count;
> -	int mode_rate, link_avail, link_clock;
>  	int common_len;
>  
>  	common_len = intel_dp_common_len_rate_limit(intel_dp,
> @@ -1766,37 +1800,22 @@ intel_dp_compute_link_config(struct intel_encoder *encoder,
>  		      intel_dp->common_rates[limits.max_clock],
>  		      limits.max_bpp, adjusted_mode->crtc_clock);
>  
> -	for (bpp = limits.max_bpp; bpp >= limits.min_bpp; bpp -= 2 * 3) {
> -		mode_rate = intel_dp_link_required(adjusted_mode->crtc_clock,
> -						   bpp);
> -
> -		for (clock = limits.min_clock; clock <= limits.max_clock; clock++) {
> -			for (lane_count = limits.min_lane_count;
> -			     lane_count <= limits.max_lane_count;
> -			     lane_count <<= 1) {
> -
> -				link_clock = intel_dp->common_rates[clock];
> -				link_avail = intel_dp_max_data_rate(link_clock,
> -								    lane_count);
> -
> -				if (mode_rate <= link_avail) {
> -					goto found;
> -				}
> -			}
> -		}
> -	}
> -
> -	return false;
> -
> -found:
> -	pipe_config->lane_count = lane_count;
> -	pipe_config->pipe_bpp = bpp;
> -	pipe_config->port_clock = intel_dp->common_rates[clock];
> +	/*
> +	 * Optimize for slow and wide. This is the place to add alternative
> +	 * optimization policy.
> +	 */
> +	if (!intel_dp_compute_link_config_wide(intel_dp, pipe_config, &limits))
> +		return false;
>  
>  	DRM_DEBUG_KMS("DP lane count %d clock %d bpp %d\n",
> -		      pipe_config->lane_count, pipe_config->port_clock, bpp);
> -	DRM_DEBUG_KMS("DP link bw required %i available %i\n",
> -		      mode_rate, link_avail);
> +		      pipe_config->lane_count, pipe_config->port_clock,
> +		      pipe_config->pipe_bpp);
> +
> +	DRM_DEBUG_KMS("DP link rate required %i available %i\n",
> +		      intel_dp_link_required(adjusted_mode->crtc_clock,
> +					     pipe_config->pipe_bpp),
> +		      intel_dp_max_data_rate(pipe_config->port_clock,
> +					     pipe_config->lane_count));

Wouldnt it be better if we move this Debug message about Available and
required link rate in the other function right after the condition
if (mode_rate <= link_avail) is true, before returning true from that function.
I think it will be just more intuitive there.

Everything else looks good. So

Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>

Manasi

>  
>  	return true;
>  }
> -- 
> 2.11.0
> 
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