[PATCH] drm/amd/display: Fix Display Flicker on embedded panels

[Harry Wentland]

On 2021-09-22 13:58, Praful.Swarnakar at amd.com wrote:
> From: Praful Swarnakar <Praful.Swarnakar at amd.com>
> 
> [Why]
> ASSR is dependent on Signed PSP Verstage to enable Content
> Protection for eDP panels. Unsigned PSP verstage is used
> during development phase causing ASSR to FAIL.
> As a result, link training is performed with
> DP_PANEL_MODE_DEFAULT instead of DP_PANEL_MODE_EDP for
> eDP panels that causes display flicker on some panels.
> 
> [How]
> - Do not change panel mode, if ASSR is disabled
> - Just report and continue to perform eDP link training
> with right settings further.
> 
> Signed-off-by: Praful Swarnakar <Praful.Swarnakar at amd.com>

Good catch. ASSR for content protection purposes requires
signed PSP but there are eDP panels that require ASSR in
order to light up correctly.

Reviewed-by: Harry Wentland <harry.wentland at amd.com>

Harry

> ---
>  drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c | 15 +++++++--------
>  1 file changed, 7 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c b/drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c
> index 6421c896f2a1..120c9955cafb 100644
> --- a/drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c
> +++ b/drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c
> @@ -2419,14 +2419,13 @@ bool perform_link_training_with_retries(
>  		if (panel_mode == DP_PANEL_MODE_EDP) {
>  			struct cp_psp *cp_psp = &stream->ctx->cp_psp;
>  
> -			if (cp_psp && cp_psp->funcs.enable_assr) {
> -				if (!cp_psp->funcs.enable_assr(cp_psp->handle, link)) {
> -					/* since eDP implies ASSR on, change panel
> -					 * mode to disable ASSR
> -					 */
> -					panel_mode = DP_PANEL_MODE_DEFAULT;
> -				}
> -			}
> +			if (cp_psp && cp_psp->funcs.enable_assr)
> +				/* ASSR is bound to fail with unsigned PSP
> +				 * verstage used during devlopment phase.
> +				 * Report and continue with eDP panel mode to
> +				 * perform eDP link training with right settings
> +				 */
> +				cp_psp->funcs.enable_assr(cp_psp->handle, link);
>  		}
>  #endif
>  
>