linux-kernel - Re: [PATCH 2/7] drm/uAPI: Add "active color format" drm property as feedback for userspace

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Date: Tue, 9 Jan 2024 22:32:18 +0000
From: Daniel Stone <daniel@...ishbar.org>
To: Andri Yngvason <andri@...vason.is>
Cc: Harry Wentland <harry.wentland@....com>, Leo Li <sunpeng.li@....com>, 
	Rodrigo Siqueira <Rodrigo.Siqueira@....com>, Alex Deucher <alexander.deucher@....com>, 
	Christian König <christian.koenig@....com>, 
	"Pan, Xinhui" <Xinhui.Pan@....com>, David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>, 
	Thomas Zimmermann <tzimmermann@...e.de>, Jani Nikula <jani.nikula@...ux.intel.com>, 
	Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>, Rodrigo Vivi <rodrigo.vivi@...el.com>, 
	Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>, amd-gfx@...ts.freedesktop.org, 
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
	intel-gfx@...ts.freedesktop.org, Simon Ser <contact@...rsion.fr>, 
	Werner Sembach <wse@...edocomputers.com>
Subject: Re: [PATCH 2/7] drm/uAPI: Add "active color format" drm property as
 feedback for userspace

Hi,

On Tue, 9 Jan 2024 at 18:12, Andri Yngvason <andri@...vason.is> wrote:
> + * active color format:
> + *     This read-only property tells userspace the color format actually used
> + *     by the hardware display engine "on the cable" on a connector. The chosen
> + *     value depends on hardware capabilities, both display engine and
> + *     connected monitor. Drivers shall use
> + *     drm_connector_attach_active_color_format_property() to install this
> + *     property. Possible values are "not applicable", "rgb", "ycbcr444",
> + *     "ycbcr422", and "ycbcr420".

How does userspace determine what's happened without polling? Will it
only change after an `ALLOW_MODESET` commit, and be guaranteed to be
updated after the commit has completed and the event being sent?
Should it send a HOTPLUG event? Other?

Cheers,
Daniel