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

On Thu, Aug 24, 2017 at 10:57:26AM +1000, Dave Airlie wrote:

quoted

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