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Message-ID: <20250722153322.GA2785882@bhelgaas>
Date: Tue, 22 Jul 2025 10:33:22 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Mario Limonciello <superm1@...nel.org>
Cc: David Airlie <airlied@...il.com>, Bjorn Helgaas <bhelgaas@...gle.com>,
	Alex Deucher <alexander.deucher@....com>,
	Christian König <christian.koenig@....com>,
	Simona Vetter <simona@...ll.ch>, Lukas Wunner <lukas@...ner.de>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	David Woodhouse <dwmw2@...radead.org>,
	Lu Baolu <baolu.lu@...ux.intel.com>, Joerg Roedel <joro@...tes.org>,
	Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
	Alex Williamson <alex.williamson@...hat.com>,
	Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>,
	"open list:DRM DRIVERS" <dri-devel@...ts.freedesktop.org>,
	open list <linux-kernel@...r.kernel.org>,
	"open list:INTEL IOMMU (VT-d)" <iommu@...ts.linux.dev>,
	"open list:PCI SUBSYSTEM" <linux-pci@...r.kernel.org>,
	"open list:VFIO DRIVER" <kvm@...r.kernel.org>,
	"open list:SOUND" <linux-sound@...r.kernel.org>,
	Daniel Dadap <ddadap@...dia.com>,
	Mario Limonciello <mario.limonciello@....com>
Subject: Re: [PATCH v9 8/9] fbcon: Use screen info to find primary device

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@....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
> > > 
> 

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