Re: [Xen-devel] [early RFC] ARM PCI Passthrough design document

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Fri, Mar 10, 2017 at 12:23:18PM +0900, Roger Pau Monné wrote:
> On Thu, Mar 09, 2017 at 07:29:34PM -0500, Konrad Rzeszutek Wilk wrote:
> > On Thu, Mar 09, 2017 at 01:26:45PM +0000, Julien Grall wrote:
> > > Hi Konrad,
> > > 
> > > On 09/03/17 11:17, Konrad Rzeszutek Wilk wrote:
> > > > On Thu, Mar 09, 2017 at 11:59:51AM +0900, Roger Pau Monné wrote:
> > > > > On Wed, Mar 08, 2017 at 02:12:09PM -0500, Konrad Rzeszutek Wilk wrote:
> > > > > > On Wed, Mar 08, 2017 at 07:06:23PM +0000, Julien Grall wrote:
> > > > > > .. this as for SR-IOV devices you need the drivers to kick the 
> > > > > > hardware
> > > > > > to generate the new bus addresses. And those (along with the BAR 
> > > > > > regions) are
> > > > > > not visible in ACPI (they are constructued dynamically).
> > > > > 
> > > > > There's already code in Xen [0] to find out the size of the BARs of 
> > > > > SR-IOV
> > > > > devices, but I'm not sure what's the intended usage of that, does it 
> > > > > need to
> > > > > happen _after_ the driver in Dom0 has done whatever magic for this to 
> > > > > work?
> > > > 
> > > > Yes. This is called via the PHYSDEVOP_pci_device_add hypercall when
> > > > the device driver in dom0 has finished "creating" the VF. See 
> > > > drivers/xen/pci.c
> > > 
> > > We are thinking to not use PHYSDEVOP_pci_device_add hypercall for ARM and 
> > > do
> > > the PCI scanning in Xen.
> > > 
> > > If I understand correctly what you said, only the PCI driver will be able 
> > > to
> > > kick SR-IOV device and Xen would not be able to detect the device until it
> > > has been fully configured. So it would mean that we have to keep
> > > PHYSDEVOP_pci_device_add around to know when Xen can use the device.
> > > 
> > > Am I correct?
> > 
> > Yes. Unless the PCI drivers come up with some other way to tell the
> > OS that oh, hey, there is this new PCI device with this BDF.
> > 
> > Or the underlaying bus on ARM can send some 'new device' information?
> 
> Hm, is this something standard between all the SR-IOV implementations, or each
> vendors have their own sauce?

Gosh, all of them have their own sauce. The only thing that is the same
is that suddenly behind the PF device there are PCI devies that are responding
to 0xcfc requests. MAgic!
> 
> Would it be possible to do this SR-IOV initialization inside of Xen, or that

Not possible inside of the Xen, unless you slurp up DPDK inside of Xen
or the Linux network drivers inside of it.

> requires ACPI information?

No ACPI information. On x86 there is no hardware notification system. It is
only by the goodwill of the PF driver kicking the Linux OS in 'scanning' the
new PCI addresses and 'discovering' the new devices.


> 
> Roger.

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