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 17:15:05 +0000
From: Andri Yngvason <andri@...vason.is>
To: Werner Sembach <wse@...edocomputers.com>
Cc: Daniel Vetter <daniel@...ll.ch>, 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>
Subject: Re: [PATCH 3/7] drm/amd/display: Add handling for new "active color
 format" property

Hi Werner,

mið., 10. jan. 2024 kl. 13:14 skrifaði Werner Sembach <wse@...edocomputers.com>:
>
> Hi,
>
> Am 10.01.24 um 14:09 schrieb Daniel Vetter:
> > On Wed, 10 Jan 2024 at 13:53, Andri Yngvason <andri@...vason.is> wrote:
> >> 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".
> > 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_ONLY
> 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. */