linux-kernel - Re: [PATCH V2 4/5] drm/vkms: Use index instead of 0 in possible crtc

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Message-ID: <20190618110920.GT12905@phenom.ffwll.local>
Date:   Tue, 18 Jun 2019 13:09:20 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Simon Ser <contact@...rsion.fr>
Cc:     Rodrigo Siqueira <rodrigosiqueiramelo@...il.com>,
        Brian Starkey <brian.starkey@....com>,
        Liviu Dudau <liviu.dudau@....com>,
        Daniel Vetter <daniel@...ll.ch>,
        Haneen Mohammed <hamohammed.sa@...il.com>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2 4/5] drm/vkms: Use index instead of 0 in possible crtc

On Tue, Jun 18, 2019 at 07:56:23AM +0000, Simon Ser wrote:
> Interestingly, even with the previous code, possible_crtcs=1 was
> exposed to userspace [1]. I think this is because of a safeguard in
> drm_crtc_init_with_planes (drm_crtc.c:284) which sets the primary and
> cursor plane's possible_crtcs to the first CRTC if zero.
> 
> If we want to warn on possible_crtcs=0, we should probably remove this
> safeguard. Checking first whether this safeguard is used by any driver
> is probably a good idea.
> 
> [1]: https://drmdb.emersion.fr/devices/f218d1242714

Yeaht it's a bit a mess, that's why I've suggested we should bite this
bullet and fix it for real. There's a bunch others such bitmasks that many
drivers seem to not set correctly.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch