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 06:29 -0500, Bjorn Helgaas wrote:
> > Indeed our host controller depends on ARM64 so maybe it would make
> > sense to move the quirk arch/arm64/kernel/pci.c; however regardless
> > why is it strictly required for a VGA device to be legacy one in order
> > to make it the default boot device?
> > i.e. couldn't we have:
> > 
> > diff --git a/drivers/gpu/vga/vgaarb.c b/drivers/gpu/vga/vgaarb.c
> > index 0f5b2dd..a6b606c 100644
> > --- a/drivers/gpu/vga/vgaarb.c
> > +++ b/drivers/gpu/vga/vgaarb.c
> > @@ -667,8 +667,7 @@ static bool vga_arbiter_add_pci_device(struct pci_dev *pdev)
> >        /* Deal with VGA default device. Use first enabled one
> >         * by default if arch doesn't have it's own hook
> >         */
> > -     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);
> >        }
> 
> I don't know enough about the VGA arbiter to answer this.  This test was
> part of the initial implementation: deb2d2ecd43d ("PCI/GPU: implement VGA
> arbitration on Linux") by Ben.

The above simply uses the first device that has memory and IO enabled
as the default device (you don't need to have a default device).

This is essentially picking up whatever device had been initialized
by the BIOS/firmware as default. This is needed for example on x86
where the BIOS tends to only initialize one device. 

I'm not sure what problem you are trying to solve here ?

Cheers,
Ben.