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Re: [PATCH v1 11/14] xen/arm: Enable the existing x86 virtual PCI support for ARM.

  • To: Stefano Stabellini <sstabellini@xxxxxxxxxx>
  • From: Rahul Singh <Rahul.Singh@xxxxxxx>
  • Date: Tue, 21 Sep 2021 13:49:33 +0000
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  • Thread-topic: [PATCH v1 11/14] xen/arm: Enable the existing x86 virtual PCI support for ARM.

Hi Stefano,

> On 16 Sep 2021, at 9:26 pm, Stefano Stabellini <sstabellini@xxxxxxxxxx> wrote:
> On Thu, 16 Sep 2021, Rahul Singh wrote:
>> Hi Stefano,
>>> On 10 Sep 2021, at 1:26 am, Stefano Stabellini <sstabellini@xxxxxxxxxx> 
>>> wrote:
>>> On Thu, 19 Aug 2021, Rahul Singh wrote:
>>>> The existing VPCI support available for X86 is adapted for Arm.
>>>> When the device is added to XEN via the hyper call
>>>> “PHYSDEVOP_pci_device_add”, VPCI handler for the config space
>>>> access is added to the Xen to emulate the PCI devices config space.
>>> This is done just for device discovery, right?
>>> Although it is currently not implemented (and I am not asking to
>>> implement it now, I am only trying to understand the architecture), it
>>> would be possible to discover all PCI devices just by walking down the
>>> PCI hierarchy by ourselves in Xen (no Dom0 interactions) given that we
>>> have an ECAM driver.
>>> I take that would be the way to implement PCI support for Dom0less?
>> It is not possible to discover PCI devices in XEN if enumeration is not done 
>> before XEN boot.
>> If boot firmware did the enumeration,  XEN will discover the PCI device.
> OK, but if the boot firmware does the enumeration, how will Xen discover
> the PCI device exactly? Will Xen discover it because the PCI device will
> be present in device tree explicitly (will have its own device tree
> node)? Or will Xen discover it by walking the PCI bus?

Yes Xen discover it by walking the PCI bus. There is already a function in XEN 
scan_pci_devices() that we can use 
to discover the PCI device for dom0less system.




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