Re: [PATCH v5 2/9] video/aperture: use generic code to figure out the vga default device

[Daniel Vetter <daniel@ffwll.ch>]

On Fri, Apr 07, 2023 at 10:54:00PM +0200, Helge Deller wrote:
> On 4/6/23 15:21, Thomas Zimmermann wrote:
> > From: Daniel Vetter <daniel.vetter@ffwll.ch>
> > 
> > Since vgaarb has been promoted to be a core piece of the pci subsystem
> > we don't have to open code random guesses anymore, we actually know
> > this in a platform agnostic way, and there's no need for an x86
> > specific hack. See also commit 1d38fe6ee6a8 ("PCI/VGA: Move vgaarb to
> > drivers/pci")
> > 
> > This should not result in any functional change, and the non-x86
> > multi-gpu pci systems are probably rare enough to not matter (I don't
> > know of any tbh). But it's a nice cleanup, so let's do it.
> > 
> > There's been a few questions on previous iterations on dri-devel and
> > irc:
> > 
> > - fb_is_primary_device() seems to be yet another implementation of
> >    this theme, and at least on x86 it checks for both
> >    vga_default_device OR rom shadowing. There shouldn't ever be a case
> >    where rom shadowing gives any additional hints about the boot vga
> >    device, but if there is then the default vga selection in vgaarb
> >    should probably be fixed. And not special-case checks replicated all
> >    over.
> > 
> > - Thomas also brought up that on most !x86 systems
> >    fb_is_primary_device() returns 0, except on sparc/parisc. But these
> >    2 special cases are about platform specific devices and not pci, so
> >    shouldn't have any interactions.
> 
> Nearly all graphics cards on parisc machines are actually PCI cards,
> but the way we handle the handover to graphics mode with STIcore doesn't
> conflicts with your planned aperture changes.
> So no problem as far as I can see for parisc...

Ah I thought sticore was some very special bus, if those can be pci cards
underneath then I guess some cleanup eventually might be a good idea? For
anything with a pci bus it's rather strange when vgaarb and
fb_is_primary_device() aren't a match ...
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch