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

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Message-ID: <3084118.iZASKD2KPV@workhorse>
Date: Thu, 11 Dec 2025 20:42:00 +0100
From: Nicolas Frattaroli <nicolas.frattaroli@...labora.com>
To: Maxime Ripard <mripard@...nel.org>
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 Tuesday, 9 December 2025 15:16:58 Central European Standard Time Maxime Ripard wrote:
> 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);
> 
> ...

I think I get what you mean: if conn_state->color_format is set, return
directly, instead of bailing out in the fallback path. I can do that.

However, `conn_state->color_format && conn_state->color_format != DRM_COLOR_FORMAT_AUTO`
is redundant now as of v5 since DRM_COLOR_FORMAT_AUTO is 0 (and
I use its falsy nature in many other places, and don't intend to
stop doing that).

> 
> Maxime
>