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

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:


     + 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@xxxxxxxxx>

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@xxxxxxxxxxxxxxx>

Thanks for your review.

Do you know when this can be applied?


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