Re: [Qemu-devel] [PATCH v5 0/5] Connect a PCIe host and graphics support to RISC-V

[Andrea Bolognani <abologna@redhat.com>]

On Wed, 2018-10-10 at 10:57 -0700, Alistair wrote:
> On 10/10/2018 05:26 AM, Andrea Bolognani wrote:
> > * what should libvirt look for to figure out whether or not a RISC-V
> >    guest will have PCI support? For aarch64 we look for the presence
> >    of the 'gpex-pcihost' device, but of course that won't work for
> >    RISC-V so we need something else;
> 
> I'm not sure what you mean here. Why can we not do the same thing with 
> RISC-V?

The gpex-pcihost device was introduced at the same time as
aarch64/virt gained PCI support, so we can probe the binary[1] and,
if the device is present, we know that aarch64/virt guests will be
able to use PCI. We cannot do the same for RISC-V for obvious
reasons: the device is already there :)

Is there any RISC-V device / property that was introduced along
with PCI support and we can use as a witness?

> > * I have succesfully started a RISC-V guest with virtio-pci devices
> >    attached but, while they show up in 'info qtree' and friends, the
> >    guest OS itself doesn't seem to recognize any of them - not even
> >    pcie.0! I'm using the guest images listed at [1] and following the
> >    corresponding instructions, but I think the BBL build (config at
> >    [2]) is missing some feature... Any ideas what we would need to
> >    add there?
> 
> I use this monolithic config: 
> https://github.com/alistair23/meta-riscv/blob/7a950aa705b439b5ec19bb6f094930888335ba7b/recipes-kernel/linux/files/freedom-u540/defconfig
> 
> It has way too much enabled, but I think if you copy the PCIe part that 
> should be enough.

Looks like there's quite a few CONFIG*PCI* options we're missing!

Rich, can you try incorporating those and kicking off a BBL build?
If I remember correctly you might also have to backport a commit or
two to make some of the options available on RISC-V, but it should
be very feasible.

[...]
> Obviously on top of that you will need to enable the VirtIO support as 
> that doesn't exist in the hardware.

Yeah, we already have that enabled and non-PCI VirtIO devices work
just fine.


[1] Not the guest, mind you: libvirt will probe each QEMU binary only
    once to reduce the overhead, so anyth
-- 
Andrea Bolognani / Red Hat / Virtualization