linux-kernel - Re: git pull] drm for v4.1-rc1

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Message-ID: <CAPeXnHsrQrkeJ3QQ6ds6yhY0C31DKqnR2uHSm9rcXdGEHBDDAg@mail.gmail.com>
Date:	Thu, 23 Apr 2015 14:56:00 -0700
From:	Matthew Garrett <matthew.garrett@...eos.com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Dave Airlie <airlied@...ux.ie>,
	Daniel Vetter <daniel.vetter@...el.com>,
	Jani Nikula <jani.nikula@...ux.intel.com>,
	DRI mailing list <dri-devel@...ts.freedesktop.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	intel-gfx <intel-gfx@...ts.freedesktop.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	Matthew Garrett <mjg59@...eos.com>
Subject: Re: git pull] drm for v4.1-rc1

On Thu, Apr 23, 2015 at 2:30 PM, Bjorn Helgaas <bhelgaas@...gle.com> wrote:

> Your i915 does not have a ROM BAR in hardware.  If the default video
> device has no ROM BAR, pci_fixup_video() sets IORESOURCE_ROM_SHADOW
> even though the resource flags are zero because the BAR itself doesn't
> exist.
>
> If IORESOURCE_ROM_SHADOW is set, pci_map_rom() assumes there's a
> shadow ROM image at 0xC0000.  Is there a shadow image even if the
> device itself doesn't have a ROM BAR?

On UEFI systems, there's no special reason to believe that there's
anything at 0xc0000 - it depends on whether a CSM got loaded or not.
Everything is awful. So...

>   int pcibios_add_device(struct pci_dev *dev)
>   {
>     if (dev-is-default-vga-device) {
>       dev->rom = 0xC0000;
>       dev->romlen = 0x20000;
>     }

I don't know what we want to do here. This is, at some level,
fundamentally wrong - however, it also wouldn't surprise me if this is
also the only copy of the video ROM we have on some UEFI systems,
especially since I believe that Windows 7 still required that there be
a legacy ROM it could use for bootloader modesetting on UEFI
platforms. So simply making this conditional on BIOS may break
existing machines. But if there *is* a ROM there then we should be
able to id it from the usual video ROM signature?
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