[PATCH] drm/vboxvideo: Add missing remove_conflicting_pci_framebuffers call

[Hans de Goede]

Hi,

On 3/26/20 12:29 PM, Daniel Vetter wrote:
> On Wed, Mar 25, 2020 at 03:43:10PM +0100, Hans de Goede wrote:
>> The vboxvideo driver is missing a call to remove conflicting framebuffers.
>>
>> Surprisingly, when using legacy BIOS booting this does not really cause
>> any issues. But when using UEFI to boot the VM then plymouth will draw
>> on both the efifb /dev/fb0 and /dev/drm/card0 (which has registered
>> /dev/fb1 as fbdev emulation).
>>
>> VirtualBox will actual display the output of both devices (I guess it is
>> showing whatever was drawn last), this causes weird artifacts because of
>> pitch issues in the efifb when the VM window is not sized at 1024x768
>> (the window will resize to its last size once the vboxvideo driver loads,
>> changing the pitch).
>>
>> Adding the missing drm_fb_helper_remove_conflicting_pci_framebuffers()
>> call fixes this.
>>
>> Cc: stable at vger.kernel.org
>> Fixes: 2695eae1f6d3 ("drm/vboxvideo: Switch to generic fbdev emulation")
>> Signed-off-by: Hans de Goede <hdegoede at redhat.com>
>> ---
>>   drivers/gpu/drm/vboxvideo/vbox_drv.c | 4 ++++
>>   1 file changed, 4 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/vboxvideo/vbox_drv.c b/drivers/gpu/drm/vboxvideo/vbox_drv.c
>> index 8512d970a09f..261255085918 100644
>> --- a/drivers/gpu/drm/vboxvideo/vbox_drv.c
>> +++ b/drivers/gpu/drm/vboxvideo/vbox_drv.c
>> @@ -76,6 +76,10 @@ static int vbox_pci_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
>>   	if (ret)
>>   		goto err_mode_fini;
>>   
>> +	ret = drm_fb_helper_remove_conflicting_pci_framebuffers(pdev, "vboxvideodrmfb");
>> +	if (ret)
>> +		goto err_irq_fini;
> 
> To avoid transient issues this should be done as early as possible,
> definitely before the drm driver starts to touch the "hw".>

Ok will fix and then push this to drm-misc-next-fixes, thank you.

> With that
> 
> Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> 
> I do wonder though why the automatic removal of conflicting framebuffers
> doesn't work, fbdev should already do that from register_framebuffer(),
> which is called somewhere in drm_fbdev_generic_setup (after a few layers).
> 
> Did you check why the two framebuffers don't conflict, and why the uefi
> one doesn't get thrown out?

I did not check, I was not aware that this check was already happening
in register_framebuffer(). So I just checked and the reason why this
is not working is because the fbdev emulation done by drm_fbdev_generic_setup
does not fill in fb_info.apertures->ranges[0] .

So fb_info.apertures->ranges[0].base is left as 0 which does not match
with the registered efifb's aperture.

We could try to fix this, but that is not entirely trivial, we would
need to pass the pci_dev pointer down into drm_fb_helper_alloc_fbi()
then and then like remove_conflicting_pci_framebuffers() does add
apertures for all IORESOURCE_MEM PCI bars, but that would conflict
with drivers which do rely on drm_fb_helper_alloc_fbi() currently
allocating one empty aperture and then actually fill that itself...

Regards,

Hans