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

[Chen, Tiejun]

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@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?

Tiejun
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