[Intel-gfx] [RFC][PATCH] gpu:drm:i915:intel_detect_pch: back to check devfn instead of check class type

[Daniel Vetter]

On Wed, Jun 25, 2014 at 10:28:21AM +0800, Chen, Tiejun wrote:
> On 2014/6/24 10:59, Zhenyu Wang wrote:
> >On 2014.06.19 17:53:51 +0800, Tiejun Chen wrote:
> >>Originally the reason to probe ISA bridge instead of Dev31:Fun0
> >>is to make graphics device passthrough work easy for VMM, that
> >>only need to expose ISA bridge to let driver know the real
> >>hardware underneath. This is a requirement from virtualization
> >>team. Especially in that virtualized environments, XEN, there
> >>is irrelevant ISA bridge in the system with that legacy qemu
> >>version specific to xen, qemu-xen-traditional. So to work
> >>reliably, we should scan through all the ISA bridge devices
> >>and check for the first match, instead of only checking the
> >>first one.
> >>
> >>But actually, qemu-xen-traditional, is always enumerated with
> >>Dev31:Fun0, 00:1f.0 as follows:
> >>
> >>hw/pt-graphics.c:
> >>
> >>intel_pch_init()
> >>     |
> >>     + pci_isa_bridge_init(bus, PCI_DEVFN(0x1f, 0), ...);
> >>
> >>so this mean that isa bridge is still represented with Dev31:Func0
> >>like the native OS. Furthermore, currently we're pushing VGA
> >>passthrough support into qemu upstream, and with some discussion,
> >>we wouldn't set the bridge class type and just expose this devfn.
> >>
> >>So we just go back to check devfn to make life normal.
> >>
> >>Signed-off-by: Tiejun Chen <tiejun.chen at intel.com>
> >
> >This was added historically when supporting graphics device passthrough.
> >Looks qemu upstream can't accept multiple ISA bridge and our PCH is always
> >on device 31: func0 as far as I know. Looks good to me.
> >
> >Reviewed-by: Zhenyu Wang <zhenyuw at linux.intel.com>
> >
> 
> Thanks for your review.
> 
> Do you know when this can be applied?

I'll hold off merging until we have buy-in from upstream quemu on a given
approach (which should work for both linux and windows).
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch