Re: [PATCH] drm/i915: Clean up HDMI deep color handling a bit

[Jani Nikula <jani.nikula@linux.intel.com>]

On Thu, 22 Aug 2019, Ville Syrjala <ville.syrjala@linux.intel.com> wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
> Reogranize the HDMI deep color state computation to just
> loop over possible bpc values. Avoids having to maintain
> so many variants of the clock etc.
>
> The current code also looks confused w.r.t. port_clock vs.
> bw_constrained. It would happily update port_clock for
> deep color but then not actually enable deep color due to
> bw_constrained being set. The new logic handles that case
> correctly.

Care to elaborate on that please?

Some nitpicking below.

>
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_hdmi.c | 82 ++++++++++-------------
>  1 file changed, 37 insertions(+), 45 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_hdmi.c b/drivers/gpu/drm/i915/display/intel_hdmi.c
> index e02f0faecf02..ed1a7afc1ffd 100644
> --- a/drivers/gpu/drm/i915/display/intel_hdmi.c
> +++ b/drivers/gpu/drm/i915/display/intel_hdmi.c
> @@ -2262,8 +2262,7 @@ static bool hdmi_deep_color_possible(const struct intel_crtc_state *crtc_state,
>  static bool
>  intel_hdmi_ycbcr420_config(struct drm_connector *connector,
>  			   struct intel_crtc_state *config,
> -			   int *clock_12bpc, int *clock_10bpc,
> -			   int *clock_8bpc)
> +			   int *clock)
>  {
>  	struct intel_crtc *intel_crtc = to_intel_crtc(config->base.crtc);
>  
> @@ -2273,10 +2272,7 @@ intel_hdmi_ycbcr420_config(struct drm_connector *connector,
>  	}
>  
>  	/* YCBCR420 TMDS rate requirement is half the pixel clock */
> -	config->port_clock /= 2;
> -	*clock_12bpc /= 2;
> -	*clock_10bpc /= 2;
> -	*clock_8bpc /= 2;
> +	*clock /= 2;
>  	config->output_format = INTEL_OUTPUT_FORMAT_YCBCR420;
>  
>  	/* YCBCR 420 output conversion needs a scaler */
> @@ -2302,10 +2298,7 @@ int intel_hdmi_compute_config(struct intel_encoder *encoder,
>  	struct drm_scdc *scdc = &connector->display_info.hdmi.scdc;
>  	struct intel_digital_connector_state *intel_conn_state =
>  		to_intel_digital_connector_state(conn_state);
> -	int clock_8bpc = pipe_config->base.adjusted_mode.crtc_clock;
> -	int clock_10bpc = clock_8bpc * 5 / 4;
> -	int clock_12bpc = clock_8bpc * 3 / 2;
> -	int desired_bpp;
> +	int bpc, clock = pipe_config->base.adjusted_mode.crtc_clock;
>  	bool force_dvi = intel_conn_state->force_audio == HDMI_AUDIO_OFF_DVI;
>  
>  	if (adjusted_mode->flags & DRM_MODE_FLAG_DBLSCAN)
> @@ -2330,15 +2323,11 @@ int intel_hdmi_compute_config(struct intel_encoder *encoder,
>  
>  	if (adjusted_mode->flags & DRM_MODE_FLAG_DBLCLK) {
>  		pipe_config->pixel_multiplier = 2;
> -		clock_8bpc *= 2;
> -		clock_10bpc *= 2;
> -		clock_12bpc *= 2;
> +		clock *= 2;
>  	}
>  
>  	if (drm_mode_is_420_only(&connector->display_info, adjusted_mode)) {
> -		if (!intel_hdmi_ycbcr420_config(connector, pipe_config,
> -						&clock_12bpc, &clock_10bpc,
> -						&clock_8bpc)) {
> +		if (!intel_hdmi_ycbcr420_config(connector, pipe_config, &clock)) {
>  			DRM_ERROR("Can't support YCBCR420 output\n");
>  			return -EINVAL;
>  		}
> @@ -2355,41 +2344,44 @@ int intel_hdmi_compute_config(struct intel_encoder *encoder,
>  				intel_conn_state->force_audio == HDMI_AUDIO_ON;
>  	}
>  
> -	/*
> -	 * Note that g4x/vlv don't support 12bpc hdmi outputs. We also need
> -	 * to check that the higher clock still fits within limits.
> -	 */
> -	if (hdmi_deep_color_possible(pipe_config, 12) &&
> -	    hdmi_port_clock_valid(intel_hdmi, clock_12bpc,
> -				  true, force_dvi) == MODE_OK) {
> -		DRM_DEBUG_KMS("picking bpc to 12 for HDMI output\n");
> -		desired_bpp = 12*3;
> -
> -		/* Need to adjust the port link by 1.5x for 12bpc. */
> -		pipe_config->port_clock = clock_12bpc;
> -	} else if (hdmi_deep_color_possible(pipe_config, 10) &&
> -		   hdmi_port_clock_valid(intel_hdmi, clock_10bpc,
> -					 true, force_dvi) == MODE_OK) {
> -		DRM_DEBUG_KMS("picking bpc to 10 for HDMI output\n");
> -		desired_bpp = 10 * 3;
> -
> -		/* Need to adjust the port link by 1.25x for 10bpc. */
> -		pipe_config->port_clock = clock_10bpc;
> -	} else {
> -		DRM_DEBUG_KMS("picking bpc to 8 for HDMI output\n");
> -		desired_bpp = 8*3;
> +	/* for 8bpc */
> +	pipe_config->port_clock = clock;
>  
> -		pipe_config->port_clock = clock_8bpc;
> -	}
> +	for (bpc = 12; bpc > 8; bpc -= 2) {

So I generally don't like loops like this. You enter the loop with 12
and 10, don't enter with 8 but assume in later code that's what you got
if not 12 or 10. And, of course, you need to initialize
pipe_config->port_clock beforehand for that case too.

Perhaps abstracting the loop to a function would help.

Now, I think this is still an improvement on the status quo, so up to
you whether to do that now or later.

> +		int port_clock;
> +
> +		if (!hdmi_deep_color_possible(pipe_config, bpc))
> +			continue;
> +
> +		/*
> +		 * Need to adjust the port link by:
> +		 *  1.5x for 12bpc
> +		 *  1.25x for 10bpc
> +		 */
> +		port_clock = clock * bpc / 8;
> +
> +		if (hdmi_port_clock_valid(intel_hdmi, port_clock,
> +					  true, force_dvi) != MODE_OK)
> +			continue;
>  
> -	if (!pipe_config->bw_constrained) {
> -		DRM_DEBUG_KMS("forcing pipe bpp to %i for HDMI\n", desired_bpp);
> -		pipe_config->pipe_bpp = desired_bpp;
> +		pipe_config->port_clock = port_clock;
> +		break;
>  	}
>  
> +	/*
> +	 * pipe_bpp could already be below 8bpc due to
> +	 * FDI bandwidth constraints. We shouldn't bump it
> +	 * back up to 8bpc in that case.
> +	 */
> +	if (pipe_config->pipe_bpp > bpc * 3)
> +		pipe_config->pipe_bpp = bpc * 3;
> +	DRM_DEBUG_KMS("picking %dbpc for HDMI output (pipe bpp: %d)\n",
                                 ^

Put a space there?

Regardless of the nitpicks,

Reviewed-by: Jani Nikula <jani.nikula@intel.com>



> +		      bpc, pipe_config->pipe_bpp);
> +
>  	if (hdmi_port_clock_valid(intel_hdmi, pipe_config->port_clock,
>  				  false, force_dvi) != MODE_OK) {
> -		DRM_DEBUG_KMS("unsupported HDMI clock, rejecting mode\n");
> +		DRM_DEBUG_KMS("unsupported HDMI clock (%d kHz), rejecting mode\n",
> +			      pipe_config->port_clock);
>  		return -EINVAL;
>  	}

-- 
Jani Nikula, Intel Open Source Graphics Center
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