linux-kernel - Re: [PATCH 2/3] drm/vc4: Don't try to initialize FBDEV if we're only bound to V3D.

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAKMK7uHBE1Qtjr2dM3U9edEfZ0mXVEjcw+hs8mF9ZkRP4Vcm=A@mail.gmail.com>
Date:   Wed, 19 Apr 2017 21:36:04 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Eric Anholt <eric@...olt.net>
Cc:     dri-devel <dri-devel@...ts.freedesktop.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] drm/vc4: Don't try to initialize FBDEV if we're only
 bound to V3D.

On Wed, Apr 19, 2017 at 7:55 PM, Eric Anholt <eric@...olt.net> wrote:
> Daniel Vetter <daniel@...ll.ch> writes:
>> On Tue, Apr 18, 2017 at 9:11 PM, Eric Anholt <eric@...olt.net> wrote:
>>> The FBDEV initialization would throw an error in dmesg, when we just
>>> want to silently not initialize fbdev on a V3D-only VC4 instance.
>>>
>>> Signed-off-by: Eric Anholt <eric@...olt.net>
>>
>> Hm, this shouldn't be an error really, you might want to hotplug more
>> connectors later on. What exactly complains?
>
> drm_fb_helper_init() throws an error if the passed in connector count is
> 0, so drm_fb_cma_helper() printks an error.

Oh, _that_ thing. The error in there is correct, but (almost) everyone
gets this parameter wrong. This isn't the max number of connectors the
fb helper will light up, but just the max number of connectors _per_
crtc when driving in hw clone mode. There's two problems with that:
- fb helpers don't support hw clone mode, we select 1:1 crtcs for each
active connector
- I mentioned that everyone gets this wrong?

If you're moderately bored it'd be great to nuke the max_connector
argument from drm_fb_helper_init, and hard-code it to 1 (with a big
comment explaining that this needs to be changed, probably with
dynamic reallocation, once someone gets around to implementing hw
clone mode).

If you're less bored, just hardcode this to 1 in vc4 and done. Plus a
TODO.rst entry would be great in that case.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch