linux-kernel - Re: [PATCH v5 05/17] drm/display: hdmi-state-helper: Act on color format DRM property

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Message-ID: <20251209-uptight-radical-chupacabra-ac3d6d@houat>
Date: Tue, 9 Dec 2025 15:16:58 +0100
From: Maxime Ripard <mripard@...nel.org>
To: Nicolas Frattaroli <nicolas.frattaroli@...labora.com>
Cc: Harry Wentland <harry.wentland@....com>, Leo Li <sunpeng.li@....com>, 
	Rodrigo Siqueira <siqueira@...lia.com>, Alex Deucher <alexander.deucher@....com>, 
	Christian König <christian.koenig@....com>, David Airlie <airlied@...il.com>, 
	Simona Vetter <simona@...ll.ch>, Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Thomas Zimmermann <tzimmermann@...e.de>, Andrzej Hajda <andrzej.hajda@...el.com>, 
	Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>, 
	Laurent Pinchart <Laurent.pinchart@...asonboard.com>, Jonas Karlman <jonas@...boo.se>, 
	Jernej Skrabec <jernej.skrabec@...il.com>, Sandy Huang <hjc@...k-chips.com>, 
	Heiko Stübner <heiko@...ech.de>, Andy Yan <andy.yan@...k-chips.com>, 
	Jani Nikula <jani.nikula@...ux.intel.com>, Rodrigo Vivi <rodrigo.vivi@...el.com>, 
	Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>, Tvrtko Ursulin <tursulin@...ulin.net>, 
	Dmitry Baryshkov <lumag@...nel.org>, Sascha Hauer <s.hauer@...gutronix.de>, 
	Rob Herring <robh@...nel.org>, kernel@...labora.com, amd-gfx@...ts.freedesktop.org, 
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, linux-rockchip@...ts.infradead.org, 
	intel-gfx@...ts.freedesktop.org, intel-xe@...ts.freedesktop.org
Subject: Re: [PATCH v5 05/17] drm/display: hdmi-state-helper: Act on color
 format DRM property

On Fri, Nov 28, 2025 at 10:05:41PM +0100, Nicolas Frattaroli wrote:
> With the introduction of the "color format" DRM property, which allows
> userspace to request a specific color format, the HDMI state helper
> should implement this.
> 
> Implement it by checking whether the property is set and set to
> something other than auto. If so, pass the requested color format, and
> otherwise set RGB.
> 
> Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@...labora.com>
> ---
>  drivers/gpu/drm/display/drm_hdmi_state_helper.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/display/drm_hdmi_state_helper.c b/drivers/gpu/drm/display/drm_hdmi_state_helper.c
> index a561f124be99..5da956bdd68c 100644
> --- a/drivers/gpu/drm/display/drm_hdmi_state_helper.c
> +++ b/drivers/gpu/drm/display/drm_hdmi_state_helper.c
> @@ -649,11 +649,21 @@ hdmi_compute_config(const struct drm_connector *connector,
>  	unsigned int max_bpc = clamp_t(unsigned int,
>  				       conn_state->max_bpc,
>  				       8, connector->max_bpc);
> +	enum hdmi_colorspace hdmi_colorspace =
> +		drm_color_format_to_hdmi_colorspace(conn_state->color_format);
>  	int ret;
>  
>  	ret = hdmi_compute_format_bpc(connector, conn_state, mode, max_bpc,
> -				      HDMI_COLORSPACE_RGB);
> +				      hdmi_colorspace);
>  	if (ret) {
> +		/* If a color format was explicitly requested, don't fall back */
> +		if (conn_state->color_format) {
> +			drm_dbg_kms(connector->dev,
> +				    "Explicitly set color format '%s' doesn't work.\n",
> +				    drm_get_color_format_name(conn_state->color_format));
> +			return ret;
> +		}
> +

I think the following would be more readable:


if (conn_state->color_format && conn_state->color_format != DRM_COLOR_FORMAT_AUTO) {
    enum hdmi_colorspace hdmi_colorspace =
        drm_color_format_to_hdmi_colorspace(conn_state->color_format);

    return hdmi_compute_format_bpc(connector, conn_state, mode, max_bpc, hdmi_colorspace)
}

ret = ret = hdmi_compute_format_bpc(connector, conn_state, mode, max_bpc,
                                    HDMI_COLORSPACE_RGB);

...

Maxime

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