linux-kernel - Re: drm: GPF in drm

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Message-ID: <CAKMK7uFYs6Y+WX5OA2HN45XMoRDY+Q_qBzH2tG2Scvu49MuQMw@mail.gmail.com>
Date:   Mon, 28 Nov 2016 07:55:39 +0100
From:   Daniel Vetter <daniel.vetter@...ll.ch>
To:     David Herrmann <dh.herrmann@...il.com>,
        Michel Dänzer <michel@...nzer.net>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        syzkaller <syzkaller@...glegroups.com>,
        David Airlie <airlied@...ux.ie>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: drm: GPF in drm_getcap

On Sat, Nov 26, 2016 at 7:22 PM, David Herrmann <dh.herrmann@...il.com> wrote:
> On Sat, Nov 26, 2016 at 7:07 PM, Dmitry Vyukov <dvyukov@...gle.com> wrote:
>> grep "card0" dmesg:
>> [    5.298617] device: 'card0': device_add
>> [    5.298946] PM: Adding info for No Bus:card0
>> [    6.436178] device: 'card0': device_add
>> [    6.436488] PM: Adding info for No Bus:card0
>>
>>
>> # ls -l /dev/dri/card0
>> crw-rw---T 1 root video 226, 0 Nov 26 18:05 /dev/dri/card0
>>
>> # ls -lt /sys/class/drm/card0/device/
>> ls: cannot access /sys/class/drm/card0/device/: No such file or directory
>>
>> # ls -lt /sys/class/drm/card0/device/driver
>> ls: cannot access /sys/class/drm/card0/device/driver: No such file or directory
>
> Looks like vgem. Something like this should help:
>
>     https://gist.github.com/dvdhrm/1bcdf4f3485aa1614a0198a7b90515e2
>
> I wonder whether it would be more appropriate to return -ENOTSUPP rather than 0.

Seems a bit overkill, but can't hurt. This is most likely a
regression, probably introduced in

commit f837297ad82480024d3ad08cd84f6670bcafa862
Author: Michel Dänzer <michel.daenzer@....com>
Date:   Mon Aug 8 16:23:39 2016 +0900

    drm: Add DRM_MODE_PAGE_FLIP_TARGET_ABSOLUTE/RELATIVE flags v2

Michel, can you pls take care of this? Either with a minimal fix, or
by adopting David's patch?

Thanks, Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch