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

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

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:
> > Hi,
> > 
> > On 02/02/17 23:06, Stefano Stabellini wrote:
> > > On Thu, 2 Feb 2017, Julien Grall wrote:
> > > > On 01/02/17 10:55, Roger Pau Monné wrote:
> > > > > On Wed, Jan 25, 2017 at 06:53:20PM +0000, Julien Grall wrote:
> > > > > > On 24/01/17 20:07, Stefano Stabellini wrote:
> > > > > > > On Tue, 24 Jan 2017, Julien Grall wrote:
> > > > For DT, I would have a fallback on mapping the root complex to DOM0 if 
> > > > we
> > > > don't support it. So DOM0 could still use PCI.
> > > > 
> > > > For ACPI, I am expecting all the platform ECAM compliant or require few
> > > > quirks. So I would mandate the support of the root complex in Xen in 
> > > > order to
> > > > get PCI supported.
> > > 
> > > Sound good. Ack.
> > 
> > I am currently rewriting the design document to take into account all the
> > comments and follow the path to have the host bridge in Xen and DOM0 will
> > get an emulated one.
> > 
> > I began to look at scanning and configuring PCI devices in Xen. Looking at
> > the PCI firmware specification, the firmware is not required to configure
> > the BAR register other than for boot and console devices. This means an
> > Operating System (or the hypervisor in our case) may have to configure some
> > devices.
> > 
> > In order to configure the BAR register, Xen would need to know where are the
> > PCI resources. On ACPI they can be found in ASL, however Xen is not able to
> > parse it. In the case of Device Tree with can retrieve the PCI resources
> > using the property "ranges".
> > 
> > I can see a couple of solutions:
> >     1# Rely on DOM0 to do the PCI configuration. This means that DOM0 should
> > see all the PCI devices and therefore will not be possible to hide from DOM0
> > if we know at boot a device will be used by a guest (i.e something similar
> > to pciback.hide but directly handled in Xen).
> 
> .. 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?

Roger.

[0] 
http://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=xen/drivers/passthrough/pci.c;h=beddd4270161b9b00b792124a770bbafe398939a;hb=HEAD#l639

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