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From: Daniel Vetter <daniel@ffwll.ch>
Date: Wed, 10 Jan 2024 14:09:32 +0100
Message-ID: <CAKMK7uGhMCwbztGdEmG4gFgpyhw6j-JFow-AaprFxcX710=qXA@mail.gmail.com>
Subject: Re: [PATCH 3/7] drm/amd/display: Add handling for new "active color
 format" property
To: Andri Yngvason <andri@yngvason.is>
Cc: Harry Wentland <harry.wentland@amd.com>, Leo Li <sunpeng.li@amd.com>, 
	Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>, Alex Deucher <alexander.deucher@amd.com>, 
	=?UTF-8?Q?Christian_K=C3=B6nig?= <christian.koenig@amd.com>, 
	"Pan, Xinhui" <Xinhui.Pan@amd.com>, David Airlie <airlied@gmail.com>, 
	Maarten Lankhorst <maarten.lankhorst@linux.intel.com>, Maxime Ripard <mripard@kernel.org>, 
	Thomas Zimmermann <tzimmermann@suse.de>, Jani Nikula <jani.nikula@linux.intel.com>, 
	Joonas Lahtinen <joonas.lahtinen@linux.intel.com>, Rodrigo Vivi <rodrigo.vivi@intel.com>, 
	Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>, amd-gfx@lists.freedesktop.org, 
	dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, 
	intel-gfx@lists.freedesktop.org, Simon Ser <contact@emersion.fr>, 
	Werner Sembach <wse@tuxedocomputers.com>
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On Wed, 10 Jan 2024 at 13:53, Andri Yngvason <andri@yngvason.is> wrote:
>
> mi=C3=B0., 10. jan. 2024 kl. 11:10 skrifa=C3=B0i Daniel Vetter <daniel@ff=
wll.ch>:
> >
> > On Tue, Jan 09, 2024 at 06:11:00PM +0000, Andri Yngvason wrote:
> > > +     /* Extract information from crtc to communicate it to userspace=
 as connector properties */
> > > +     for_each_new_connector_in_state(state, connector, new_con_state=
, i) {
> > > +             struct drm_crtc *crtc =3D new_con_state->crtc;
> > > +             struct dc_stream_state *stream;
> > > +
> > > +             if (crtc) {
> > > +                     new_crtc_state =3D drm_atomic_get_new_crtc_stat=
e(state, crtc);
> > > +                     dm_new_crtc_state =3D to_dm_crtc_state(new_crtc=
_state);
> > > +                     stream =3D dm_new_crtc_state->stream;
> > > +
> > > +                     if (stream) {
> > > +                             drm_connector_set_active_color_format_p=
roperty(connector,
> > > +                                     convert_dc_pixel_encoding_into_=
drm_color_format(
> > > +                                             dm_new_crtc_state->stre=
am->timing.pixel_encoding));
> > > +                     }
> > > +             } else {
> > > +                     drm_connector_set_active_color_format_property(=
connector, 0);
> >
> > Just realized an even bigger reason why your current design doesn't wor=
k:
> > You don't have locking here.
> >
> > And you cannot grab the required lock, which is
> > drm_dev->mode_config.mutex, because that would result in deadlocks. So
> > this really needs to use the atomic state based design I've described.
> >
>
> Maybe we should just drop "actual color format" and instead fail the
> modeset if the "preferred color format" property cannot be satisfied?
> It seems like the simplest thing to do here, though it is perhaps less
> convenient for userspace. In that case, the "preferred color format"
> property should just be called "color format".

Yeah that's more in line with how other atomic properties work. This
way userspace can figure out what works with a TEST_ONLY commit too.
And for this to work you probably want to have an "automatic" setting
too.
-Sima
--=20
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch