Re: [PATCH v9 8/9] fbcon: Use screen info to find primary device

[Bjorn Helgaas <helgaas@kernel.org>]

On Tue, Jul 22, 2025 at 09:45:28AM -0500, Mario Limonciello wrote:
> On 7/22/25 9:38 AM, Bjorn Helgaas wrote:
> > On Thu, Jul 17, 2025 at 12:38:11PM -0500, Mario Limonciello wrote:
> > > From: Mario Limonciello <mario.limonciello@amd.com>
> > > 
> > > On systems with non VGA GPUs fbcon can't find the primary GPU because
> > > video_is_primary_device() only checks the VGA arbiter.
> > > 
> > > Add a screen info check to video_is_primary_device() so that callers
> > > can get accurate data on such systems.
> > 
> > This relies on screen_info, which I think is an x86 BIOS-ism.  Isn't
> > there a UEFI console path?  How does that compare with this?  Is that
> > relevant or is it something completely different?
> 
> When I created and tested this I actually did this on a UEFI system (which
> provides a UEFI GOP driver).

I guess screen_info is actually *not* an x86 BIOS-ism, and on UEFI
systems, we do actually rely on UEFI, e.g., in efi_setup_gop(),
alloc_screen_info(), init_screen_info()?

But this patch is x86-specific, so I'm guessing the same problem could
occur on arm64, Loongson, or other UEFI platforms, and this series
doesn't address those?

> > >   bool video_is_primary_device(struct device *dev)
> > >   {
> > > +#ifdef CONFIG_SCREEN_INFO
> > > +	struct screen_info *si = &screen_info;
> > > +#endif
> > >   	struct pci_dev *pdev;
> > >   	if (!dev_is_pci(dev))
> > > @@ -34,7 +38,18 @@ bool video_is_primary_device(struct device *dev)
> > >   	pdev = to_pci_dev(dev);
> > > -	return (pdev == vga_default_device());
> > > +	if (!pci_is_display(pdev))
> > > +		return false;
> > > +
> > > +	if (pdev == vga_default_device())
> > > +		return true;
> > > +
> > > +#ifdef CONFIG_SCREEN_INFO
> > > +	if (pdev == screen_info_pci_dev(si))
> > > +		return true;
> > > +#endif
> > > +
> > > +	return false;
> > >   }
> > >   EXPORT_SYMBOL(video_is_primary_device);
> > > -- 
> > > 2.43.0
> > > 
>