linux-kernel - Re: [PATCH 2/2] samples: rust: fix endianness issue in rust_driver

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Message-ID: <cac484ba-904b-447d-b802-3e324c843ffe@gmail.com>
Date: Wed, 10 Dec 2025 15:10:12 +0100
From: Dirk Behme <dirk.behme@...il.com>
To: Marko Turk <mt@...koturk.info>, dakr@...nel.org, bhelgaas@...gle.com,
 kwilczynski@...nel.org, miguel.ojeda.sandonis@...il.com,
 dirk.behme@...bosch.com, linux-pci@...r.kernel.org,
 linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org
Subject: Re: [PATCH 2/2] samples: rust: fix endianness issue in
 rust_driver_pci

On 10.12.25 12:25, Marko Turk wrote:
> MMIO backend of PCI Bar always assumes little-endian devices and
> will convert to CPU endianness automatically. Remove the u32::from_le
> conversion which would cause a bug on big-endian machines.
> 
> Signed-off-by: Marko Turk <mt@...koturk.info>
> Fixes: 685376d18e9a ("samples: rust: add Rust PCI sample driver")
> ---
>  samples/rust/rust_driver_pci.rs | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/samples/rust/rust_driver_pci.rs b/samples/rust/rust_driver_pci.rs
> index 5823787bea8e..fa677991a5c4 100644
> --- a/samples/rust/rust_driver_pci.rs
> +++ b/samples/rust/rust_driver_pci.rs
> @@ -48,7 +48,7 @@ fn testdev(index: &TestIndex, bar: &Bar0) -> Result<u32> {
>          // Select the test.
>          bar.write8(index.0, Regs::TEST);
>  
> -        let offset = u32::from_le(bar.read32(Regs::OFFSET)) as usize;
> +        let offset = bar.read32(Regs::OFFSET) as usize;

Yes, dropping from_le() is what we talked about:

Reviewed-by: Dirk Behme <dirk.behme@...bosch.com>

Thanks

Dirk

P.S.: I'm not sure if the `Fixes` is required: As far as I understood
there are no big-endian machines supported by Rust, yet. On all other
supported little-endian machines this is a no-op. So I think it is at
least debatable if this is a "bug" which needs back porting.