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

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Message-ID: <20260126122021.1c617ea2.zhiw@nvidia.com>
Date: Mon, 26 Jan 2026 12:21:13 +0200
From: Zhi Wang <zhiw@...dia.com>
To: Alexandre Courbot <acourbot@...dia.com>
CC: <rust-for-linux@...r.kernel.org>, <linux-pci@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <dakr@...nel.org>, <aliceryhl@...gle.com>,
	<bhelgaas@...gle.com>, <kwilczynski@...nel.org>, <ojeda@...nel.org>,
	<alex.gaynor@...il.com>, <boqun.feng@...il.com>, <gary@...yguo.net>,
	<bjorn3_gh@...tonmail.com>, <lossin@...nel.org>, <a.hindborg@...nel.org>,
	<tmgross@...ch.edu>, <markus.probst@...teo.de>, <helgaas@...nel.org>,
	<cjia@...dia.com>, <smitra@...dia.com>, <ankita@...dia.com>,
	<aniketa@...dia.com>, <kwankhede@...dia.com>, <targupta@...dia.com>,
	<joelagnelf@...dia.com>, <jhubbard@...dia.com>, <zhiwang@...nel.org>,
	<daniel.almeida@...labora.com>
Subject: Re: [PATCH v12 5/5] sample: rust: pci: add tests for config space
 routines

On Mon, 26 Jan 2026 09:05:31 +0000
Zhi Wang <zhiw@...dia.com> wrote:

> On Mon, 26 Jan 2026 14:08:30 +0900
> "Alexandre Courbot" <acourbot@...dia.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@...nel.org>
> > >> Signed-off-by: Zhi Wang <zhiw@...dia.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

The dmesg in the VM:

[    2.762517] rust_driver_pci 0000:00:04.0: pci-testdev data-match count:1 
[    2.764368] rust_driver_pci 0000:00:04.0: pci-testdev config space
read8 rev ID: 0 
[    2.766478] rust_driver_pci 0000:00:04.0: pci-testdev
config space read16 vendor ID: 1b36
[    2.770523] rust_driver_pci
0000:00:04.0: pci-testdev config space read32 BAR 0: febd2000

Z.