linux-kernel - Re: [PATCH 3/3] drm/connector: hdmi: Use YUV420 output format as an RGB fallback

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Message-ID: <w66zx533ugdapxvs6mtks7wj3tyqdu334t33mbb6i665m2fiqk@r4qtm7linuvv>
Date: Sat, 30 Nov 2024 10:39:46 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Cristian Ciocaltea <cristian.ciocaltea@...labora.com>
Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, kernel@...labora.com, 
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] drm/connector: hdmi: Use YUV420 output format as an
 RGB fallback

On Sat, Nov 30, 2024 at 01:56:34AM +0200, Cristian Ciocaltea wrote:
> Introduce the switch to YUV420 when computing the best output format and
> RGB cannot be supported for a given color depth.
> 
> While at it, add a minor improvement to the debug message indicating the
> supported format.
> 
> Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@...labora.com>
> ---
>  drivers/gpu/drm/display/drm_hdmi_state_helper.c | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/display/drm_hdmi_state_helper.c b/drivers/gpu/drm/display/drm_hdmi_state_helper.c
> index 3a55881a544a519bb1254968db891c814f831a0f..b4e865e0680f35fd2d849536789f6c1f98a48258 100644
> --- a/drivers/gpu/drm/display/drm_hdmi_state_helper.c
> +++ b/drivers/gpu/drm/display/drm_hdmi_state_helper.c
> @@ -304,7 +304,7 @@ hdmi_try_format_bpc(const struct drm_connector *connector,
>  		return false;
>  	}
>  
> -	drm_dbg_kms(dev, "%s output format supported with %u (TMDS char rate: %llu Hz)\n",
> +	drm_dbg_kms(dev, "%s output format supported with %u bpc (TMDS char rate: %llu Hz)\n",

Correct, but irrelevant. Please split to a separate commit.

>  		    drm_hdmi_connector_get_output_format_name(fmt),
>  		    bpc, conn_state->hdmi.tmds_char_rate);
>  
> @@ -319,15 +319,16 @@ hdmi_compute_format(const struct drm_connector *connector,
>  {
>  	struct drm_device *dev = connector->dev;
>  
> -	/*
> -	 * TODO: Add support for YCbCr420 output for HDMI 2.0 capable
> -	 * devices, for modes that only support YCbCr420.
> -	 */
>  	if (hdmi_try_format_bpc(connector, conn_state, mode, bpc, HDMI_COLORSPACE_RGB)) {
>  		conn_state->hdmi.output_format = HDMI_COLORSPACE_RGB;
>  		return 0;
>  	}
>  
> +	if (hdmi_try_format_bpc(connector, conn_state, mode, bpc, HDMI_COLORSPACE_YUV420)) {
> +		conn_state->hdmi.output_format = HDMI_COLORSPACE_YUV420;
> +		return 0;
> +	}

Should we prefer YCbCr 4:2:0 over RGB?

> +
>  	drm_dbg_kms(dev, "Failed. No Format Supported for that bpc count.\n");
>  
>  	return -EINVAL;
> 
> -- 
> 2.47.0
> 

-- 
With best wishes
Dmitry