Regression: drm: Lobotomize set_busid nonsense for !pci drivers (a325725633c2)

[Emil Velikov]

Hi all

On 30 September 2016 at 04:09, Laszlo Ersek <lersek at redhat.com> wrote:
> Hello Daniel,
>
> On 06/21/16 14:08, daniel.vetter at ffwll.ch (Daniel Vetter) wrote:
>> We already have a fallback in place to fill out the unique from
>> dev->unique, which is set to something reasonable in drm_dev_alloc.
>>
>> Which means we only need to have a special set_busid for pci devices,
>> to be able to care the backwards compat code for drm 1.1 around, which
>> libdrm still needs.
>>
>> While developing and testing this patch things blew up in really
>> interesting ways, and the code is rather confusing in naming things
>> between the kernel code, ioctl #defines and libdrm. For the next brave
>> dragon slayer, document all this madness properly in the userspace
>> interface section of gpu.tmpl.
>>
>> v2: Make drm_dev_set_unique static and update kerneldoc.
>>
>> v3: Entire rewrite, plus document what's going on for posterity in the
>> gpu docbook uapi section.
>>
>> v4: Drop accidental amdgpu hunk (Emil).
>>
>> v5: Drop accidental omapdrm vblank counter change (Emil).
>>

> This patch (commit a325725633c2) regresses X.org on QEMU's virtio-vga
> device. Please see
>
>   https://bugzilla.redhat.com/show_bug.cgi?id=1366842
>
> complete with a bisection log under
>
>   drivers/gpu/drm/virtio/
>
Having gone through the xserver code as this patch was written, I'm
not entrirely sure how this can happen.

Since there is a very nice cleanup series that this patch is build
upon, I'd suggest trying to understand the issue, rather than a blind
revert.

Here we want to check the xserver/libdrm codepath before/after the
kernel patch, in particular the following drmOpen, drmAvailable,
drmSetInterfaceVersion and drmGetBusid. If the xserver is using open()
with drmSetInterfaceVersion then that is _not_ something it should be
doing and I'm against working around it in the kernel (fwiw).

To ease things one can set LIBGL_DEBUG=verbose (yay fun name) and
libdrm will print out some debug output to stderr

Regards,
Emil