Re: [PATCH v12 5/5] sample: rust: pci: add tests for config space routines

["Alexandre Courbot" <acourbot@nvidia.com>]

On Mon Jan 26, 2026 at 6:05 PM JST, Zhi Wang wrote:
> On Mon, 26 Jan 2026 14:08:30 +0900
> "Alexandre Courbot" <acourbot@nvidia.com> wrote:
>
>> On Thu Jan 22, 2026 at 1:31 PM JST, Alexandre Courbot wrote:
>> > On Thu Jan 22, 2026 at 5:22 AM JST, Zhi Wang wrote:
>> >> Add tests exercising the PCI configuration space helpers.
>> >>
>> >> Suggested-by: Danilo Krummrich <dakr@kernel.org>
>> >> Signed-off-by: Zhi Wang <zhiw@nvidia.com>
>> >> ---
>> >>  samples/rust/rust_driver_pci.rs | 28 ++++++++++++++++++++++++++++
>> >>  1 file changed, 28 insertions(+)
>> >>
>> >> diff --git a/samples/rust/rust_driver_pci.rs
>> >> b/samples/rust/rust_driver_pci.rs index 38c949efce38..1bc5bd1a8df5
>> >> 100644 --- a/samples/rust/rust_driver_pci.rs
>> >> +++ b/samples/rust/rust_driver_pci.rs
>> >> @@ -5,6 +5,7 @@
>> >>  //! To make this driver probe, QEMU must be run with `-device
>> >> pci-testdev`. 
>> >>  use kernel::{
>> >> +    device::Bound,
>> >>      device::Core,
>> >>      devres::Devres,
>> >>      io::Io,
>> >> @@ -65,6 +66,32 @@ fn testdev(index: &TestIndex, bar: &Bar0) ->
>> >> Result<u32> { 
>> >>          Ok(bar.read32(Regs::COUNT))
>> >>      }
>> >> +
>> >> +    fn config_space(pdev: &pci::Device<Bound>) -> Result {
>> >> +        let config = pdev.config_space()?;
>> >> +
>> >> +        // TODO: use the register!() macro for defining PCI
>> >> configuration space registers once it
>> >
>> > I'll rebase the `register!` series on top of this and try to address
>> > this item.
>> 
>> Actually... is this expected to work?
>> 
>> > +        dev_info!(
>> > +            pdev.as_ref(),
>> > +            "pci-testdev config space read8 rev ID: {:x}\n",
>> > +            config.read8(0x8)
>> > +        );
>> 
>> We are performing I/O on `config`, but since this is a sample device
>> with no hardware backing, what is providing the data for the
>> registers?
>> 
>
> We are running the sample driver in the virtual machine. QEMU provides
> a emulated PCI test device (-device pci-testdev) for this purpose. E.g.
> with the following command line, I am able to run and test this in the
> virtual machine.
>
> qemu-system-x86_64 \
>         -enable-kvm \
>         -cpu host \
>         -m 8192 \
>         -smp 24 \
>         -drive file=/home/inno/vm/xubuntu.img,if=virtio \
>         -netdev user,id=net0 \
>         -device virtio-net-pci,netdev=net0 \
>         -device usb-tablet \
>         -device pci-testdev \
>         -usb

Ah, that makes sense! Thanks for the explanation.