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Date:   Mon, 29 Mar 2021 16:39:02 +0100
From:   Paul Cercueil <paul@crapouillou.net>
Subject: Re: [PATCH] drm: DON'T require each CRTC to have a unique primary
 plane
To:     Maxime Ripard <maxime@cerno.tech>
Cc:     Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        Simon Ser <contact@emersion.fr>, od@zcrc.me,
        dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org,
        stable@vger.kernel.org
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Le lun. 29 mars 2021 ? 17:35, Maxime Ripard <maxime@cerno.tech> a 
?crit :
> On Mon, Mar 29, 2021 at 04:15:28PM +0100, Paul Cercueil wrote:
>>  Hi Maxime,
>> 
>>  Le lun. 29 mars 2021 ? 16:07, Maxime Ripard <maxime@cerno.tech> a 
>> ?crit :
>>  > On Sat, Mar 27, 2021 at 11:22:14AM +0000, Paul Cercueil wrote:
>>  > >  The ingenic-drm driver has two mutually exclusive primary 
>> planes
>>  > >  already; so the fact that a CRTC must have one and only one 
>> primary
>>  > >  plane is an invalid assumption.
>>  >
>>  > I mean, no? It's been documented for a while that a CRTC should 
>> only
>>  > have a single primary, so I'd say that the invalid assumption was 
>> that
>>  > it was possible to have multiple primary planes for a CRTC.
>> 
>>  Documented where?
>> 
>>  I did read the doc of "enum drm_plane_type" in <drm/drm_plane.h>, 
>> and the
>>  DRM_PLANE_TYPE_PRIMARY describes my two planes, so I went with that.
> 
> At least since 4.9, this was in the documentation generated for DRM:
> https://elixir.bootlin.com/linux/v4.9.263/source/drivers/gpu/drm/drm_plane.c#L43

Ok, I read that as "all drivers should provide AT LEAST one primary 
plane per CRTC", and not as "all drivers should provide ONE AND ONLY 
ONE primary plane per CRTC". My bad.

-Paul