Re: [Intel-gfx] [PATCH 7/8] video/aperture: Only remove sysfb on the default vga pci device

[Javier Martinez Canillas <javierm@redhat.com>]

Daniel Vetter <daniel.vetter@ffwll.ch> writes:

> Instead of calling aperture_remove_conflicting_devices() to remove the
> conflicting devices, just call to aperture_detach_devices() to detach
> the device that matches the same PCI BAR / aperture range. Since the
> former is just a wrapper of the latter plus a sysfb_disable() call,
> and now that's done in this function but only for the primary devices.
>
> This fixes a regression introduced by ee7a69aa38d8 ("fbdev: Disable
> sysfb device registration when removing conflicting FBs"), where we
> remove the sysfb when loading a driver for an unrelated pci device,
> resulting in the user loosing their efifb console or similar.
>
> Note that in practice this only is a problem with the nvidia blob,
> because that's the only gpu driver people might install which does not
> come with an fbdev driver of it's own. For everyone else the real gpu
> driver will restore a working console.
>
> Also note that in the referenced bug there's confusion that this same
> bug also happens on amdgpu. But that was just another amdgpu specific
> regression, which just happened to happen at roughly the same time and
> with the same user-observable symptoms. That bug is fixed now, see
> https://bugzilla.kernel.org/show_bug.cgi?id=216331#c15
>
> Note that we should not have any such issues on non-pci multi-gpu
> issues, because I could only find two such cases:
> - SoC with some external panel over spi or similar. These panel
>   drivers do not use drm_aperture_remove_conflicting_framebuffers(),
>   so no problem.
> - vga+mga, which is a direct console driver and entirely bypasses all
>   this.
>
> For the above reasons the cc: stable is just notionally, this patch
> will need a backport and that's up to nvidia if they care enough.
>
> v2:
> - Explain a bit better why other multi-gpu that aren't pci shouldn't
>   have any issues with making all this fully pci specific.
>
> v3
> - polish commit message (Javier)
>
> Fixes: ee7a69aa38d8 ("fbdev: Disable sysfb device registration when removing conflicting FBs")
> Tested-by: Aaron Plattner <aplattner@nvidia.com>
> Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
> References: https://bugzilla.kernel.org/show_bug.cgi?id=216303#c28
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> Cc: Aaron Plattner <aplattner@nvidia.com>
> Cc: Javier Martinez Canillas <javierm@redhat.com>
> Cc: Thomas Zimmermann <tzimmermann@suse.de>
> Cc: Helge Deller <deller@gmx.de>
> Cc: Sam Ravnborg <sam@ravnborg.org>
> Cc: Alex Deucher <alexander.deucher@amd.com>
> Cc: <stable@vger.kernel.org> # v5.19+ (if someone else does the backport)
> ---
>  drivers/video/aperture.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)

Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>

-- 
Best regards,

Javier Martinez Canillas
Core Platforms
Red Hat