[PATCH v2 1/1] Split VGA default device handler out of VGA arbiter

[Bjorn Helgaas]

On Thu, Aug 24, 2017 at 10:57:26AM +1000, Dave Airlie wrote:
> > Yeah, maybe it's time to disconnect the "default display device" idea
> > from the VGA arbiter.  I have no idea what (if any) dependencies X has
> > on the legacy VGA resources.  I assume X works fine on power, where it
> > sounds like those resources are rarely or never available.
> 
> The question on non-x86 archs, is what is the correct device to default to.
> 
> On x86 we use the legacy VGA resources as a pointer, as this is the device
> the BIOS appeared on at boot so hopefully should be one you can see stuff on.
> 
> On non-x86 I've no idea how to decide if there are multiple devices, maybe the
> firmware needs to tag something for the kernel if there are. Otherwise
> you'd just
> be picking something in probe order.
> 
> I think the idea of these patches is to separate default display
> device from the arbiter.
> 
> X uses the arbiter on x86 if required (it's horrible, and it's rare we
> have to nowadays),
> but for finding the default device it justs uses the sysfs boot_vga flag.

The sysfs boot_vga thing comes from PCI.  The name suggests that it's
a VGA device and can use the legacy VGA resources.

If we want to indicate a general default display device that need not
be "VGA", it'd be really nice if we could pick a name that did not
include "vga".

Even if we could only do it inside the kernel, I think it would reduce
confusion if we could separate out the "VGA"-specific stuff like the
arbiter and names like "vga_set_default_device()" so that systems with
a non-legacy VGA default display device didn't have to use "VGA"
interfaces that don't make sense for them.

Bjorn