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
