On 10.06.2021 17:33, Oleksandr Andrushchenko wrote: > On 10.06.21 17:10, Roger Pau Monné wrote: >> On Thu, Jun 10, 2021 at 10:01:16AM +0000, Oleksandr Andrushchenko wrote: >>> On 10.06.21 10:54, Roger Pau Monné wrote: >>>> On Fri, Jun 04, 2021 at 06:37:27AM +0000, Oleksandr Andrushchenko wrote: >>>>> Hi, all! >>>>> >>>>> While working on PCI SR-IOV support for ARM I started porting [1] on top >>>>> of current PCI on ARM support [2]. The question I have for this series >>>>> is if we really need emulating SR-IOV code in Xen? >>>>> >>>>> I have implemented a PoC for SR-IOV on ARM [3] (please see the top 2 >>>>> patches) >>>>> and it "works for me": MSI support is still WIP, but I was able to see >>>>> that >>>>> VFs are properly seen in the guest and BARs are properly programmed in >>>>> p2m. >>>>> >>>>> What I can't fully understand is if we can live with this approach or >>>>> there >>>>> are use-cases I can't see. >>>>> >>>>> Previously I've been told that this approach might not work on FreeBSD >>>>> running >>>>> as Domain-0, but is seems that "PCI Passthrough is not supported >>>>> (Xen/FreeBSD)" >>>>> anyways [4]. >>>> PCI passthorgh is not supported on FreeBSD dom0 because PCI >>>> passthrough is not supported by Xen itself when using a PVH dom0, and >>>> that's the only mode FreeBSD dom0 can use. >>> So, it is still not clear to me: how and if PCI passthrough is supported >>> >>> on FreeBSD, what are the scenarios and requirements for that? >>> >>>> PHYSDEVOP_pci_device_add can be added to FreeBSD, so it could be made >>>> to work. I however think this is not the proper way to implement >>>> SR-IOV support. >>> I was not able to find any support for PHYSDEVOP_XXX in FreeBSD code, >>> >>> could you please point me to where are these used? >> Those are not used on FreeBSD, because x86 PVHv2 dom0 doesn't >> implement them anymore. They are implemented on Linux for x86 PV dom0, >> AFAIK Arm doesn't use them either. > > Well, ARM didn't until we started implementing PCI passthrough [1]. > > It was previously discussed [2], "# Discovering PCI devices:" and proposed > > to use PHYSDEVOP_pci_device_add. > > Long story short, it is not easy for ARM to enumerate PCI devices in Xen as > there is > > no unified way of doing so: different platforms implement different PCI host > bridges > > which require complex initialization including clocks, power domains etc.
Just for my own understanding: If this isn't done by firmware, doesn't this mean you can't boot an Arm system from e.g. a disk connected through a PCI-based controller? Host bridge setup is definitely firmware's job on x86 ... Jan
