[PATCH] drm/vboxvideo: Add missing remove_conflicting_pci_framebuffers call

[Daniel Vetter]

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". 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?
-Daniel

> +
>  	ret = drm_fbdev_generic_setup(&vbox->ddev, 32);
>  	if (ret)
>  		goto err_irq_fini;
> -- 
> 2.26.0.rc2
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch