[Intel-gfx] [PATCH] drm/i915: Don't overestimate 4:2:0 link symbol clock

[Mun, Gwan-gyeong]

On Wed, 2019-07-10 at 15:58 +0300, Ville Syrjala wrote:
> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> 
> With 4:2:0 output the LS clock can be half of what it is with 4:4:4.
> Make that happen.
> 
> Cc: Gwan-gyeong Mun <gwan-gyeong.mun at intel.com>
> Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dp.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c
> b/drivers/gpu/drm/i915/display/intel_dp.c
> index 0bdb7ecc5a81..1dfacf090fb8 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -1853,8 +1853,10 @@ intel_dp_compute_link_config_wide(struct
> intel_dp *intel_dp,
>  	int mode_rate, link_clock, link_avail;
>  
>  	for (bpp = limits->max_bpp; bpp >= limits->min_bpp; bpp -= 2 *
> 3) {
> +		int output_bpp = intel_dp_output_bpp(pipe_config, bpp);
> +
>  		mode_rate = intel_dp_link_required(adjusted_mode-
> >crtc_clock,
> -						   bpp);
> +						   output_bpp);
>  
>  		for (clock = limits->min_clock; clock <= limits-
> >max_clock; clock++) {
>  			for (lane_count = limits->min_lane_count;
According to DP 1.4 spec section 1.7.1 [Makeup of the Main-Link],
previous implementation worked by below explaination.
After the stream data is packed and mapped to the Main-Link, the packed
stream data rate shall be less than or equal to the Main-Link’s link
symbol rate. When the packed stream data rate is less than the Main-
Link’s link symbol rate, stuffing symbols are inserted.

Reviewed-by: Gwan-gyeong Mun <gwan-gyeong.mun at intel.com>
Tested-by: Gwan-gyeong Mun <gwan-gyeong.mun at intel.com>