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Re: [Xen-devel] [Query] Assigning PCI ranges to dom0 and domU

On Fri, 1 Aug 2014, Stefano Stabellini wrote:
> On Fri, 1 Aug 2014, manish jaggi wrote:
> > Hi Stefano,
> > 
> > I am working on accessing PCI nodes in the doms on ARM (cavium). If there 
> > is the below device tree nodeÂ
> > pcie1@0x849000000000 {
> > ÂÂÂ ÂÂÂÂÂÂÂ compatible = "cavium,thunder-pcie";
> > ÂÂÂ ÂÂÂ device_type = "pci";
> > ÂÂÂ ÂÂÂ msi-parent = <&its>;
> > ÂÂÂ ÂÂÂ bus-range = <0 255>;
> > ÂÂÂ ÂÂÂ #size-cells = <2>;
> > ÂÂÂ ÂÂÂ #address-cells = <3>;
> > ÂÂÂÂÂÂÂ ÂÂÂ reg = <0x8490 0x00000000 0 0x40000000>;Â /* Configuration space 
> > */
> > ÂÂÂ ÂÂÂ ranges = <0x03000000 0x8310 0x00000000 0x8310 0x00000000 0x00 
> > 0x10000000>, /* mem ranges */
> > ÂÂÂ ÂÂÂ ÂÂÂ <0x03000000 0x8100 0x00000000 0x8100 0x00000000 0x80 
> > 0x00000000>;
> > ÂÂÂÂÂÂÂ };
> > ÂÂÂ
> > 
> > How to assign ranges to guest dom0 / domU. Is there a well defined api in 
> > xen OR I have to parse the device tree
> > ranges and do a 1:1 mapping using map_mmio_regions.
> Firstly you just need to get PCI up and running in Dom0, and you can do
> that by passing this device tree node to Dom0 and remapping the
> appropriate memory ranges. See for example:
> xen/arch/arm/platforms/xgene-storm.c:xgene_storm_specific_mapping

So yes, to reply to your specific question, you need to parse the device
tree and use map_mmio_regions for Dom0.

For DomU, the toolstack allows the guest to map the mmio regions of the
device by calling xc_domain_iomem_permission.
On ARM in addition to that you'll have to add those MMIO regions to the
guest p2m, otherwise the guest won't still have access to them. (x86 PV
guests don't actually have a proper p2m, like ARM guests do, so giving
them permission would be enough.)

> Once that is done, it is time to look at pciback and pcifront and try to
> get them running on ARM.
> I would start by enabling PCI passthrough in the xl toolstack, look at
> tools/libxl/libxl_pci.c:libxl__device_pci_add, called by
> domcreate_attach_pci. It should be working on ARM following the PV path
> After the toolstack parts are in place, you should be able to see a pci
> entry in xenstore (xenstore-ls to list everything that is present in
> xenstore). That is the basic information needed by pcifront and pciback
> to enstablish a communication channel. Pcifront is
> drivers/pci/xen-pcifront.c and pciback is drivers/xen/xen-pciback: you
> need to compile and initialize them on ARM. You might have to implement
> a few ARM  specific missing pieces, corresponding to the x86 ones in
> arch/x86/pci/xen.c. They are mostly about MSIs.
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