On Mon, Jan 30, 2017 at 10:45:22AM -0700, Alex Williamson wrote: > On Mon, 30 Jan 2017 09:15:50 +0100 > Gerd Hoffmann <kraxel@xxxxxxxxxx> wrote: > > > Hi, > > > > > The vgaarb code has a concept of a vga_default_device(), it's rather > > > PCI-centric, but maybe better than nothing. This is typically the > > > first VGA class code device found with I/O and MMIO enabled. If fbcon > > > defaulted to running on the vga_default_device(), a user could select > > > which to use by re-ordering the VM hardware. > > > > The qemu drivers don't register as vgaarb clients though. Which easily > > explains why igd always wins the primary selection, no matter how you > > order your hardware. > > > > So, should they register? The drivers don't need access to the vga > > registers[1][2]. > > The VGA arbiter sets up a notifier on the PCI bus and will add any VGA > class code devices it finds. So even if the driver doesn't > participate, it'll still be tracked and might be marked as primary. If > a graphics driver claims a VGA device that does not depend on VGA > region access then the driver should configure the device not to claim > VGA accesses (maybe only relevant for integrated graphics - i915 gets > this wrong), and register with the arbiter to opt-out of VGA > arbitration. Picking a "primary" can be done w/o any of that latter if > we agree on the arbiter algorithm of picking the first device with VGA > routing to it (or it can be overridden by arch/platform code). Thanks, Fyi we don't get this wrong, we indeed need vga access in some cases. Broken hw :( The other issue is that the X server asks for vga access (or at least did in the past) for every render op, even if it's a kms driver. Which makes X crawl if you have multi-gpu system. Those two things combined means vgaarb is essentially dead on any system with intel gfx. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
