Re: [Intel-gfx] [PATCH v5 1/5] x86/quirks: Fix stolen detection with integrated + discrete GPU

[Bjorn Helgaas <helgaas@kernel.org>]

On Wed, Jan 19, 2022 at 12:30:04PM -0800, Lucas De Marchi wrote:
> On Tue, Jan 18, 2022 at 02:01:45PM -0600, Bjorn Helgaas wrote:

> > Haha :)  I was hoping not to touch it myself because I think this
> > whole stolen memory thing is kind of nasty.  It's not clear to me why
> > we need it at all, or why we have to keep all this device-specific
> > logic in the kernel, or why it has to be an early quirk as opposed to
> > a regular PCI quirk.  We had a thread [1] about it a while ago but I
> > don't think anything got resolved.
> 
> I was reading that thread again and thinking what we could do to try to
> resolve this. I will reply on that thread.

Great!  I hope there's some way around this.

> > But to try to make forward progress, I applied patch 1/5 (actually,
> > the updated one from [2]) to my pci/misc branch with the updated
> > commit log and code comments below.
> 
> thanks. I found the wording in the title odd as when I read "first" it
> gives me the impression it's saying there could be more, which is not
> possible.

I said "first integrated GPU" because Linux doesn't control what
devices are in the system; it just has to deal with whatever it finds.
All one can tell from the code is that if we find one or more devices
that appear in intel_early_ids[], we reserve stolen memory for the
first such device.

System-specific knowledge might tell you that there should only be one
integrated GPU, but there's no constraint like that in Linux.

Bjorn