linux-kernel - Re: [PATCH 3/7] drm/amd/display: Add handling for new "active color format" property

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Date: Wed, 10 Jan 2024 12:52:46 +0000
From: Andri Yngvason <andri@...vason.is>
To: Andri Yngvason <andri@...vason.is>, 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>, 
	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>
Cc: Daniel Vetter <daniel@...ll.ch>
Subject: Re: [PATCH 3/7] drm/amd/display: Add handling for new "active color
 format" property

mið., 10. jan. 2024 kl. 11:10 skrifaði Daniel Vetter <daniel@...ll.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 = new_con_state->crtc;
> > +             struct dc_stream_state *stream;
> > +
> > +             if (crtc) {
> > +                     new_crtc_state = drm_atomic_get_new_crtc_state(state, crtc);
> > +                     dm_new_crtc_state = to_dm_crtc_state(new_crtc_state);
> > +                     stream = dm_new_crtc_state->stream;
> > +
> > +                     if (stream) {
> > +                             drm_connector_set_active_color_format_property(connector,
> > +                                     convert_dc_pixel_encoding_into_drm_color_format(
> > +                                             dm_new_crtc_state->stream->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 work:
> 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".

Thanks,
Andri