On 3 October 2016 at 18:08, Laszlo Ersek <lersek@xxxxxxxxxx> wrote:
> On 10/03/16 18:43, Emil Velikov wrote:
>> Earlier commit was removing all the users of drm_platform_set_busid and
>> removed the virtio hunk (which uses the PCI version of the function) by
>> mistake.
>>
>> This in itself resulted in user space receiving an incorrect value for
>> the busid, which in the case below lead to the failure to detect
>> the (correct) device and ultimately the X server failing to start.
>>
>> Fixes: a325725633c ("drm: Lobotomize set_busid nonsense for !pci
>> drivers")
>> Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
>> Cc: Laszlo Ersek <lersek@xxxxxxxxxx>
>> Cc: stable@xxxxxxxxxxxxxxx
>> Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1366842
>> Reported-by: Laszlo Ersek <lersek@xxxxxxxxxx>
>> Signed-off-by: Emil Velikov <emil.l.velikov@xxxxxxxxx>
>> ---
>> Since I'm not 100% sure if we can get into .set_busid() as pci_dev is
>> NULL (for the virtio-vga 'vs' virgio-gpu-pci case) I've left the local
>> wrapper.
>>
>> Note: patch is against mainline (refs/tags/v4.8) but should apply for
>> drm-next/others.
>> ---
>> drivers/gpu/drm/virtio/virtgpu_drm_bus.c | 10 ++++++++++
>> drivers/gpu/drm/virtio/virtgpu_drv.c | 1 +
>> drivers/gpu/drm/virtio/virtgpu_drv.h | 1 +
>> 3 files changed, 12 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/virtio/virtgpu_drm_bus.c b/drivers/gpu/drm/virtio/virtgpu_drm_bus.c
>> index 7f0e93f87..88a3916 100644
>> --- a/drivers/gpu/drm/virtio/virtgpu_drm_bus.c
>> +++ b/drivers/gpu/drm/virtio/virtgpu_drm_bus.c
>> @@ -27,6 +27,16 @@
>>
>> #include "virtgpu_drv.h"
>>
>> +int drm_virtio_set_busid(struct drm_device *dev, struct drm_master *master)
>> +{
>> + struct pci_dev *pdev = dev->pdev;
>> +
>> + if (pdev) {
>> + return drm_pci_set_busid(dev, master);
>> + }
>> + return 0;
>> +}
>> +
>> static void virtio_pci_kick_out_firmware_fb(struct pci_dev *pci_dev)
>> {
>> struct apertures_struct *ap;
>> diff --git a/drivers/gpu/drm/virtio/virtgpu_drv.c b/drivers/gpu/drm/virtio/virtgpu_drv.c
>> index c13f70c..5820b702 100644
>> --- a/drivers/gpu/drm/virtio/virtgpu_drv.c
>> +++ b/drivers/gpu/drm/virtio/virtgpu_drv.c
>> @@ -117,6 +117,7 @@ static const struct file_operations virtio_gpu_driver_fops = {
>>
>> static struct drm_driver driver = {
>> .driver_features = DRIVER_MODESET | DRIVER_GEM | DRIVER_PRIME | DRIVER_RENDER | DRIVER_ATOMIC,
>> + .set_busid = drm_virtio_set_busid,
>> .load = virtio_gpu_driver_load,
>> .unload = virtio_gpu_driver_unload,
>> .open = virtio_gpu_driver_open,
>> diff --git a/drivers/gpu/drm/virtio/virtgpu_drv.h b/drivers/gpu/drm/virtio/virtgpu_drv.h
>> index b18ef31..acf556a 100644
>> --- a/drivers/gpu/drm/virtio/virtgpu_drv.h
>> +++ b/drivers/gpu/drm/virtio/virtgpu_drv.h
>> @@ -49,6 +49,7 @@
>> #define DRIVER_PATCHLEVEL 1
>>
>> /* virtgpu_drm_bus.c */
>> +int drm_virtio_set_busid(struct drm_device *dev, struct drm_master *master);
>> int drm_virtio_init(struct drm_driver *driver, struct virtio_device *vdev);
>>
>> struct virtio_gpu_object {
>>
>
> I've come up with the identical patch (code-wise). I haven't posted it yet because:
> - I'd like to reproduce the original issue with the fresh 4.8 kernel, using the F24 config (so the build is taking forever :( :( :(),
> - I'd like to test the patch too.
>
> Obviously, testing your patch is just as good as testing my (identical) patch, it's just that I'll have to respond with a Tested-by.
>
> However, my commit message is different; what do you think of it?
>
> --------
> commit a005c99587ce52b60cfae897071f124cc5867347
> Author: Laszlo Ersek <lersek@xxxxxxxxxx>
> Date: Mon Oct 3 17:59:14 2016 +0200
>
> drm: virtio: reinstate drm_virtio_set_busid()
>
> Before commit a325725633c2 ("drm: Lobotomize set_busid nonsense for !pci
> drivers"), several DRM drivers for platform devices used to expose an
> explicit "drm_driver.set_busid" callback, invariably backed by
> drm_platform_set_busid().
>
> Commit a325725633c2 removed drm_platform_set_busid(), along with the
> referring .set_busid field initializations. This was justified because
> interchangeable functionality had been implemented in drm_dev_alloc() /
> drm_dev_init(), which DRM_IOCTL_SET_VERSION would rely on going forward.
>
> However, commit a325725633c2 also removed drm_virtio_set_busid(), for
> which the same consolidation was not appropriate: this .set_busid callback
> had been implemented with drm_pci_set_busid(), and not
> drm_platform_set_busid(). The error regressed Xorg/xserver on QEMU's
> "virtio-vga" card; the drmGetBusid() function from libdrm would no longer
> return stable PCI identifiers like "pci:0000:00:02.0", but rather unstable
> platform ones like "virtio0".
>
> Reinstate drm_virtio_set_busid() with judicious use of
>
> git checkout -p a325725633c2^ -- drivers/gpu/drm/virtio
>
> Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
> Cc: Daniel Vetter <daniel.vetter@xxxxxxxxx>
> Cc: David Airlie <airlied@xxxxxxxxxx>
> Cc: Emil Velikov <emil.l.velikov@xxxxxxxxx>
> Cc: Gerd Hoffmann <kraxel@xxxxxxxxxx>
> Cc: Gustavo Padovan <gustavo.padovan@xxxxxxxxxxxxxxx>
> Cc: Hans de Goede <hdegoede@xxxxxxxxxx>
> Cc: Joachim Frieben <jfrieben@xxxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> Reported-by: Joachim Frieben <jfrieben@xxxxxxxxxxx>
> Fixes: a325725633c26aa66ab940f762a6b0778edf76c0
> Ref: https://bugzilla.redhat.com/show_bug.cgi?id=1366842
> Signed-off-by: Laszlo Ersek <lersek@xxxxxxxxxx>
>
> drivers/gpu/drm/virtio/virtgpu_drm_bus.c | 10 ++++++++++
> drivers/gpu/drm/virtio/virtgpu_drv.c | 1 +
> drivers/gpu/drm/virtio/virtgpu_drv.h | 1 +
> 3 files changed, 12 insertions(+)
> --------
>
> I obviously don't "insist" that you take my commit message :), but you might want to scavenge it for some bits. You might not as well. :)
>
Your commit message sounds a lot better, so I'd go with it (it even
provides the exact same steps I used to revert the virtio-gpu hunks).
Feel free to add:
Reviewed-by: Emil Velikov <emil.l.velikov@xxxxxxxxx>
> Regarding the local wrapper around drm_pci_set_busid(): that's not because of virtio-vga vs. virtio-gpu-pci. Instead, it's due to the virtio-mmio vs. virtio-pci transports that are possible for virtio devices. Theoretically at least, a virtio-gpu device could be exposed by QEMU as a memory mapped device in arm/arm64 guests. In that case the "platform bus ID" would simply be the base address of the virtio-mmio register block.
>
> In practice, virtio-gpu over virtio-mmio would be an extremely outlandish configuration (noone does / should do that, plain and simple). Which is why implementing actual "platform bus ID" logic for the virtio-mmio transport case is unnecessary. It's just that the kernel shouldn't crash even if someone tries virtio-gpu over virtio-mmio.
>
> So, the wrapper function (with the pdev nullity check) should be preserved, even if not entirely for the reason you suspected.
>
> Anyway, my laptop seems to have ceased emitting sounds resembling a gas turbine, which I'll take as the completion of the 4.8 kernel build. Will be back soon with test results...
>
Ack, my virtio terminology is a bit sub par ;-)
Fwiw you could do a quick verification and hack a local libdrm.so
LD_PRELOAD-ing it ;-)
Either way, thanks for the report and for the well spotted thinko (/me
still cannot believe he did not see it)
Emil
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