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> -- Open Source Technology Center, Intel ltd. $gpg --keyserver wwwkeys.pgp.net --recv-keys 4D781827
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