Re: [Xen-devel] [PATCH for-2.10 1/2] hw/acpi: Call acpi_set_pci_info when no ACPI tables needed

["Michael S. Tsirkin" <mst@xxxxxxxxxx>]

On Mon, Aug 14, 2017 at 03:55:50PM +0100, Anthony PERARD wrote:
> On Fri, Aug 11, 2017 at 08:18:28PM +0300, Michael S. Tsirkin wrote:
> > On Fri, Aug 11, 2017 at 04:11:37PM +0100, Anthony PERARD wrote:
> > > To do PCI passthrough with Xen, the property acpi-pcihp-bsel needs to be
> > > set, but this was done only when ACPI tables are built which is not
> > > needed for a Xen guest. The need for the property starts with commit
> > > "pc: pcihp: avoid adding ACPI_PCIHP_PROP_BSEL twice"
> > > (f0c9d64a68b776374ec4732424a3e27753ce37b6).
> > > 
> > > Set pci info before checking for the needs to build ACPI tables.
> > > 
> > > Reported-by: Sander Eikelenboom <linux@xxxxxxxxxxxxxx>
> > > Tested-by: Sander Eikelenboom <linux@xxxxxxxxxxxxxx>
> > > Signed-off-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
> > 
> > I am worried that Xen will come to depend on specific
> > assignment of bsel which isn't guaranteed. Thoughts on
> > how to avoid that?
> 
> Is it possible to have a different BSEL than 0 with PIIX ?

With PCI to PCI bridges, yes.

> Also, I don't known if having more than on PCI bus is going to work on
> Xen, there is nothing in our ACPI tables beyond _SB.PCI0, and nothing to
> use a different BSEL.

My worry is someone might decide to implement hotplug for pci to pci
bridges on Xen. If doing that, it's important to use the qemu supplied
acpi tables.

> > > 
> > > ---
> > > In this patch rather than always calling acpi_set_pci_info() when
> > > acpi_setup() is called, we could check first for acpi_enabled? (which is
> > > true for Xen.)
> > 
> > Yes, please change it like this. Also, please add
> > a comment explainging what it does.
> 
> Will do.
> 
> -- 
> Anthony PERARD

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