[PATCH v2] drm/amd/display: add a check for display depth validity

[Harry Wentland]

On 2018-07-04 05:27 PM, mikita.lipski at amd.com wrote:
> From: Mikita Lipski <mikita.lipski at amd.com>
> 
> [why]
> HDMI 2.0 fails to validate 4K at 60 timing with 10 bpc
> [how]
> Adding a helper function that would verify if the display depth
> assigned would pass a bandwidth validation.
> Drop the display depth by one level till calculated pixel clk
> is lower than maximum TMDS clk.
> 

It'd be good to include a brief description what changed in v2. Something like

v2: check_if_display_depth_is_supported -> adjust_colour_depth_from_display_info

> Bugzilla: https://bugs.freedesktop.org/106959
> 
> Signed-off-by: Mikita Lipski <mikita.lipski at amd.com>

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

Harry

> ---
>  drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 42 +++++++++++++++++++++++
>  1 file changed, 42 insertions(+)
> 
> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> index 9529043..a0f1b1d 100644
> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> @@ -2218,6 +2218,46 @@ get_output_color_space(const struct dc_crtc_timing *dc_crtc_timing)
>  	return color_space;
>  }
>  
> +static void reduce_mode_colour_depth(struct dc_crtc_timing *timing_out)
> +{
> +	if (timing_out->display_color_depth <= COLOR_DEPTH_888)
> +		return;
> +
> +	timing_out->display_color_depth--;
> +}
> +
> +static void adjust_colour_depth_from_display_info(struct dc_crtc_timing *timing_out,
> +						const struct drm_display_info *info)
> +{
> +	int normalized_clk;
> +	if (timing_out->display_color_depth <= COLOR_DEPTH_888)
> +		return;
> +	do {
> +		normalized_clk = timing_out->pix_clk_khz;
> +		/* YCbCr 4:2:0 requires additional adjustment of 1/2 */
> +		if (timing_out->pixel_encoding == PIXEL_ENCODING_YCBCR420)
> +			normalized_clk /= 2;
> +		/* Adjusting pix clock following on HDMI spec based on colour depth */
> +		switch (timing_out->display_color_depth) {
> +		case COLOR_DEPTH_101010:
> +			normalized_clk = (normalized_clk * 30) / 24;
> +			break;
> +		case COLOR_DEPTH_121212:
> +			normalized_clk = (normalized_clk * 36) / 24;
> +			break;
> +		case COLOR_DEPTH_161616:
> +			normalized_clk = (normalized_clk * 48) / 24;
> +			break;
> +		default:
> +			return;
> +		}
> +		if (normalized_clk <= info->max_tmds_clock)
> +			return;
> +		reduce_mode_colour_depth(timing_out);
> +
> +	} while (timing_out->display_color_depth > COLOR_DEPTH_888);
> +
> +}
>  /*****************************************************************************/
>  
>  static void
> @@ -2274,6 +2314,8 @@ fill_stream_properties_from_drm_display_mode(struct dc_stream_state *stream,
>  
>  	stream->out_transfer_func->type = TF_TYPE_PREDEFINED;
>  	stream->out_transfer_func->tf = TRANSFER_FUNCTION_SRGB;
> +	if (stream->sink->sink_signal == SIGNAL_TYPE_HDMI_TYPE_A)
> +		adjust_colour_depth_from_display_info(timing_out, info);
>  }
>  
>  static void fill_audio_info(struct audio_info *audio_info,
>