On Mon, 02 June 2014 Bruno Pr?mont <bonbons at linux-vserver.org> wrote:
> With commit b4aa0163056b ("efifb: Implement vga_default_device() (v2)")
> Matthew Garrett introduced a efifb vga_default_device() so that EFI
> systems that do not load shadow VBIOS or setup VGA get proper value for
> boot_vga PCI sysfs attribute on the corresponding PCI device.
>
> Xorg is refusing to detect devices when boot_vga=0 which is the case on
> some EFI system (e.g. MacBookAir2,1). Xorg detects the GPU and finds
> the dri device but then bails out with "no devices detected".
>
> Note: When vga_default_device() is set boot_vga PCI sysfs attribute
> reflects its state. When unset this attribute is 1 whenever
> IORESOURCE_ROM_SHADOW flag is set.
>
> With introduction of sysfb/simplefb/simpledrm efifb is getting obsolete
> while having native drivers for the GPU also makes selecting
> sysfb/efifb optional.
>
> Remove the efifb implementation of vga_default_device() and initialize
> vgaarb's vga_default_device() with the PCI GPU that matches boot
> screen_info in pci_fixup_video().
Quite a few people trip over this issue, apparently concentrated on
Apple Macs (EFI) with Nvidia graphics.
It has shown up in at least two bugzilla reports (as side-issue):
https://bugs.freedesktop.org/show_bug.cgi?id=58556#c16
https://bugs.freedesktop.org/show_bug.cgi?id=76732#c34
My initial report and discussion on freenode, #nouveau:
http://people.freedesktop.org/~cbrill/dri-log/?channel=nouveau&date=2013-11-23
followed by initial patch proposal:
http://permalink.gmane.org/gmane.comp.video.dri.devel/95943
