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From: Andri Yngvason <andri@yngvason.is>
Date: Wed, 10 Jan 2024 17:15:05 +0000
Message-ID: <CAFNQBQyg+yXSJRtZtyHXMfyBOYrQpU0R0XFUJLcof9rakrBYQA@mail.gmail.com>
Subject: Re: [PATCH 3/7] drm/amd/display: Add handling for new "active color
 format" property
To: Werner Sembach <wse@tuxedocomputers.com>
Cc: Daniel Vetter <daniel@ffwll.ch>, 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>
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Hi Werner,

mi=C3=B0., 10. jan. 2024 kl. 13:14 skrifa=C3=B0i Werner Sembach <wse@tuxedo=
computers.com>:
>
> Hi,
>
> Am 10.01.24 um 14:09 schrieb Daniel Vetter:
> > 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=
@ffwll.ch>:
> >>> On Tue, Jan 09, 2024 at 06:11:00PM +0000, Andri Yngvason wrote:
> >>>> +     /* Extract information from crtc to communicate it to userspac=
e as connector properties */
> >>>> +     for_each_new_connector_in_state(state, connector, new_con_stat=
e, 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_sta=
te(state, crtc);
> >>>> +                     dm_new_crtc_state =3D to_dm_crtc_state(new_crt=
c_state);
> >>>> +                     stream =3D 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->str=
eam->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 w=
ork:
> >>> 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. S=
o
> >>> 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
>
> The problem with TEST_ONLY probing is that color format settings are
> interdependent: https://gitlab.freedesktop.org/drm/amd/-/issues/476#note_=
966634
>
> So changing any other setting may require every color format to be TEST_O=
NLY
> probed again.
>

If we put a bit map containing the possible color formats into
drm_mode_mode_info (I'm thinking that it could go into flags), we'd be
able to eliminate a bunch of combinations early on. Do you think that
would make things more bearable?

I'm thinking, something like this:
diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
index 128d09138ceb3..59980803cb89e 100644
--- a/include/uapi/drm/drm_mode.h
+++ b/include/uapi/drm/drm_mode.h
@@ -124,6 +124,13 @@ extern "C" {
 #define  DRM_MODE_FLAG_PIC_AR_256_135 \
                        (DRM_MODE_PICTURE_ASPECT_256_135<<19)

+/* Possible color formats (4 bits) */
+#define DRM_MODE_FLAG_COLOR_FORMAT_MASK (0x0f << 22)
+#define DRM_MODE_FLAG_COLOR_FORMAT_RGB (1 << 22)
+#define DRM_MODE_FLAG_COLOR_FORMAT_YCBCR444 (1 << 23)
+#define DRM_MODE_FLAG_COLOR_FORMAT_YCBCR422 (1 << 24)
+#define DRM_MODE_FLAG_COLOR_FORMAT_YCBCR420 (1 << 25)
+
 #define  DRM_MODE_FLAG_ALL     (DRM_MODE_FLAG_PHSYNC |         \
                                 DRM_MODE_FLAG_NHSYNC |         \
                                 DRM_MODE_FLAG_PVSYNC |         \
@@ -136,7 +143,8 @@ extern "C" {
                                 DRM_MODE_FLAG_HSKEW |          \
                                 DRM_MODE_FLAG_DBLCLK |         \
                                 DRM_MODE_FLAG_CLKDIV2 |        \
-                                DRM_MODE_FLAG_3D_MASK)
+                                DRM_MODE_FLAG_3D_MASK |        \
+                                DRM_MODE_FLAG_COLOR_FORMAT_MASK)

 /* DPMS flags */
 /* bit compatible with the xorg definitions. */