linux-kernel - Re: [PATCH v4 06/23] drm/connector: hdmi: Use YUV420 output format as an RGB fallback

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Message-ID: <amnwcb3sxo7nbfobag3v2ojowqvrpqqkqykg3qfhxwxzp5olur@fibxgdcs2mee>
Date: Tue, 13 May 2025 15:35:35 +0200
From: Maxime Ripard <mripard@...nel.org>
To: Cristian Ciocaltea <cristian.ciocaltea@...labora.com>
Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, 
	Simona Vetter <simona@...ll.ch>, Dave Stevenson <dave.stevenson@...pberrypi.com>, 
	Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>, Dmitry Baryshkov <lumag@...nel.org>, kernel@...labora.com, 
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 06/23] drm/connector: hdmi: Use YUV420 output format
 as an RGB fallback

Hi,

On Fri, Apr 25, 2025 at 01:26:57PM +0300, Cristian Ciocaltea wrote:
> Try to make use of YUV420 when computing the best output format and
> RGB cannot be supported for any of the available color depths.
> 
> Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@...labora.com>
> ---
>  drivers/gpu/drm/display/drm_hdmi_state_helper.c | 22 +++++++++++++++++-----
>  1 file changed, 17 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 9e0a468073acbb2477eff1abef1c09d63620afaa..1fba10b92a6baa49150b6ff1e96bf2c2739bf269 100644
> --- a/drivers/gpu/drm/display/drm_hdmi_state_helper.c
> +++ b/drivers/gpu/drm/display/drm_hdmi_state_helper.c
> @@ -648,14 +648,26 @@ hdmi_compute_config(const struct drm_connector *connector,
>  				       8, connector->max_bpc);
>  	int ret;
>  
> -	/*
> -	 * TODO: Add support for YCbCr420 output for HDMI 2.0 capable
> -	 * devices, for modes that only support YCbCr420.
> -	 */
>  	ret = hdmi_compute_format_bpc(connector, conn_state, mode, max_bpc,
>  				      HDMI_COLORSPACE_RGB);
> +	if (!ret)
> +		return 0;

Sorry, I missed it on the previous iteration, but this condition
inversion compared to the rest of the function is throwing me off :)

I believe something like

If (ret) {
   if (connector->ycbcr_420_allowed) {
      hdmi_compute_format_bpc(..., HDMI_COLORSPACE_YUV420)
   } else {
     drm_dbg_kms("Can't use YUV420")
   }
}

Would be more natural

Maxime

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