linux-kernel - Re: [PATCH v4 6/7] sample: rust: pci: use `register!` macro

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Message-ID: <20260128143522.434f75f6.zhiw@nvidia.com>
Date: Wed, 28 Jan 2026 14:35:22 +0200
From: Zhi Wang <zhiw@...dia.com>
To: Alexandre Courbot <acourbot@...dia.com>
CC: Danilo Krummrich <dakr@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>,
	Daniel Almeida <daniel.almeida@...labora.com>, Miguel Ojeda
	<ojeda@...nel.org>, Boqun Feng <boqun.feng@...il.com>, Gary Guo
	<gary@...yguo.net>, Björn Roy Baron
	<bjorn3_gh@...tonmail.com>, Benno Lossin <lossin@...nel.org>, "Andreas
 Hindborg" <a.hindborg@...nel.org>, Trevor Gross <tmgross@...ch.edu>, "Yury
 Norov" <yury.norov@...il.com>, John Hubbard <jhubbard@...dia.com>, "Alistair
 Popple" <apopple@...dia.com>, Joel Fernandes <joelagnelf@...dia.com>, "Timur
 Tabi" <ttabi@...dia.com>, Edwin Peer <epeer@...dia.com>, Eliot Courtney
	<ecourtney@...dia.com>, Dirk Behme <dirk.behme@...bosch.com>, Steven Price
	<steven.price@....com>, <rust-for-linux@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 6/7] sample: rust: pci: use `register!` macro

On Wed, 28 Jan 2026 11:37:32 +0900
Alexandre Courbot <acourbot@...dia.com> wrote:

> Convert the direct IO accesses to properly defined registers.
> 

Tested-by: Zhi Wang <zhiw@...dia.com>

I can see the correct value of the registers read by the sample driver
from the demesg. 

Additionally, Clippy was complaining about unnecssary unsafe blocks and
can be fixed by: (I haven't fully gone through the code, just applied this
for getting rid of the warnnings.)

diff --git a/rust/kernel/num/bounded.rs b/rust/kernel/num/bounded.rs
index 850827033f67..efabdd31ec37 100644
--- a/rust/kernel/num/bounded.rs
+++ b/rust/kernel/num/bounded.rs
@@ -503,9 +503,7 @@ pub fn cast<U>(self) -> Bounded<U, N>
     pub fn shr<const SHIFT: u32, const RES: u32>(self) -> Bounded<T, RES>
{ const { assert!(RES >= N - SHIFT) }

-        // SAFETY: We shift the value right by `SHIFT`, reducing the
  number of bits needed to
-        // represent the shifted value by as much, and just asserted that
  `RES == N - SHIFT`.
-        unsafe { Bounded::__new(self.0 >> SHIFT) }
+        Bounded::__new(self.0 >> SHIFT)
     }

     /// Left-shifts `self` by `SHIFT` and returns the result as a
     `Bounded<_, RES>`, where `RES >= @@ -524,9 +522,7 @@ pub fn shr<const
     SHIFT: u32, const RES: u32>(self) -> Bounded<T, RES> { pub fn
     shl<const SHIFT: u32, const RES: u32>(self) -> Bounded<T, RES> {
     const { assert!(RES >= N + SHIFT) }

-        // SAFETY: We shift the value left by `SHIFT`, augmenting the
  number of bits needed to
-        // represent the shifted value by as much, and just asserted that
  `RES == N + SHIFT`.
-        unsafe { Bounded::__new(self.0 << SHIFT) }
+        Bounded::__new(self.0 << SHIFT)
     }
 }

Z.

> Signed-off-by: Alexandre Courbot <acourbot@...dia.com>
> ---
>  samples/rust/rust_driver_pci.rs | 23 ++++++++++++++++++-----
>  1 file changed, 18 insertions(+), 5 deletions(-)
> 
> diff --git a/samples/rust/rust_driver_pci.rs
> b/samples/rust/rust_driver_pci.rs index 4dfb8a6a4707..df2232d6b71f 100644
> --- a/samples/rust/rust_driver_pci.rs
> +++ b/samples/rust/rust_driver_pci.rs
> @@ -70,24 +70,37 @@ fn testdev(index: &TestIndex, bar: &Bar0) ->
> Result<u32> { fn config_space(pdev: &pci::Device<Bound>) {
>          let config = pdev.config_space();
>  
> -        // TODO: use the register!() macro for defining PCI
> configuration space registers once it
> -        // has been move out of nova-core.
> +        // Some PCI configuration space registers.
> +        ::kernel::register! {
> +            VENDOR_ID(u16) @ 0x0 {
> +                15:0 vendor_id;
> +            }
> +
> +            REVISION_ID(u8) @ 0x8 {
> +                7:0 revision_id;
> +            }
> +
> +            BAR(u32)[6] @ 0x10 {
> +                31:0 value;
> +            }
> +        }
> +
>          dev_info!(
>              pdev.as_ref(),
>              "pci-testdev config space read8 rev ID: {:x}\n",
> -            config.read8(0x8)
> +            REVISION_ID::read(&&config).revision_id()
>          );
>  
>          dev_info!(
>              pdev.as_ref(),
>              "pci-testdev config space read16 vendor ID: {:x}\n",
> -            config.read16(0)
> +            VENDOR_ID::read(&&config).vendor_id()
>          );
>  
>          dev_info!(
>              pdev.as_ref(),
>              "pci-testdev config space read32 BAR 0: {:x}\n",
> -            config.read32(0x10)
> +            BAR::read(&&config, 0).value()
>          );
>      }
>  }
>