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

[Daniel Vetter <daniel@ffwll.ch>]

On Tue, Apr 04, 2023 at 01:59:33PM -0700, Aaron Plattner wrote:
> On 4/4/23 1:18 PM, Daniel Vetter wrote:
> > 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.
> 
> It might be worth noting that this also affects devices that have no driver
> installed, or where the driver failed to initialize or was configured not to
> set a mode. E.g. I reproduced this problem on a laptop with i915.modeset=0
> and an NVIDIA driver that calls drm_fbdev_generic_setup. It would also
> reproduce on a system that sets modeset=0 (or has a GPU that's too new for
> its corresponding kernel driver) and that passes an NVIDIA GPU through to a
> VM using vfio-pci since that also calls
> aperture_remove_conflicting_pci_devices.
> 
> I agree that in practice this will mostly affect people with our driver
> until I get my changes to add drm_fbdev_generic_setup checked in. But these
> other cases don't seem all that unlikely to me.

Thomas Z. refactored the entire modeset=0 handling to be more consistent
across drivers, so I think in practice it'll again only happen with the
nvidia blob driver (unless you patch in the call to
drm_firmware_drivers_only()). Or if you dont use nomodeset or similar and
instead use a driver-specific module option, which isn't what howtos in
distros recommend.

I can add this to the commit message if you want?
-Daniel

> 
> -- Aaron
> 
> > 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(-)
> > 
> > diff --git a/drivers/video/aperture.c b/drivers/video/aperture.c
> > index 8f1437339e49..2394c2d310f8 100644
> > --- a/drivers/video/aperture.c
> > +++ b/drivers/video/aperture.c
> > @@ -321,15 +321,16 @@ int aperture_remove_conflicting_pci_devices(struct pci_dev *pdev, const char *na
> >   	primary = pdev == vga_default_device();
> > +	if (primary)
> > +		sysfb_disable();
> > +
> >   	for (bar = 0; bar < PCI_STD_NUM_BARS; ++bar) {
> >   		if (!(pci_resource_flags(pdev, bar) & IORESOURCE_MEM))
> >   			continue;
> >   		base = pci_resource_start(pdev, bar);
> >   		size = pci_resource_len(pdev, bar);
> > -		ret = aperture_remove_conflicting_devices(base, size, name);
> > -		if (ret)
> > -			return ret;
> > +		aperture_detach_devices(base, size);
> >   	}
> >   	if (primary) {

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch