Re: [PATCH v4] PCI: Support hibmc VGA cards behind a misbehaving HiSilicon bridge

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Thu, 2017-07-13 at 15:11 -0600, Alex Williamson wrote:
> > >       */
> > > -   if (vga_default == NULL &&
> > > -       ((vgadev->owns & VGA_RSRC_LEGACY_MASK) == VGA_RSRC_LEGACY_MASK)) {
> > > +   if (vga_default == NULL) {
> > >              vgaarb_info(&pdev->dev, "setting as boot VGA device\n");
> > >              vga_set_default_device(pdev);
> > >      }  
> 
> 
> "Legacy" is the breadcrumb we use to try to pick the same device for
> default VGA as the system firmware used as the boot VGA.  There can be
> multiple VGA devices in the system, the change above would simply make
> the first discovered device be the default VGA.  That would break many,
> many systems.  If legacy VGA ranges mean nothing on ARM64, then follow
> the powerpc lead and make an arch quirk that simply selects the first
> enabled VGA device as the default.  VGA routing is part of the PCI spec
> though, so the default of selecting the device with routing enabled
> makes sense.  Thanks,

"Legacy" there iirc also means that it has decoding enabled at boot. If
you pick the first one you may pick a device that doesn't and hasn't
been initialized by any driver (good old BIOS-initialized text mode).

Cheers,
Ben.