Re: [PATCH] samples: rust: fix endianness issue in rust_driver_pci

["Danilo Krummrich" <dakr@kernel.org>]

On Wed Nov 12, 2025 at 8:56 PM AEDT, Miguel Ojeda wrote:
> I guess we could potentially consider something like returning a
> wrapper to force us to explicitly pick either LE or BE to prevent
> things like this.

In general, the I/O backend (e.g. MMIO, I2C, etc.) is supposed to take care
of endianness.

In the case of MMIO we (currently) always assume that the device is
little-endian; this is also what the C functions used to implement the MMIO
backend (e.g. readl()) assume, i.e. they always convert from little-endian to
CPU endianness.

I don't think we should do anything else; the cases where we need to deal with
big-endian devices for MMIO should be extremely rare -- rare enough that there
aren't even corresponding *_be() implementations for all architectures.

Given that, I think the proper fix is to drop the existing u32::from_le() call
(that ended up in the sample driver by accident) and properly document the
little-endian assumption of the MMIO backend.

(Currently, this simply is the Io structure, but there is a patch series [1]
from Zhi splitting things up, so we can start supporting arbitrary I/O
backends.)

@Marko: Two separate patches for this would be very welcome. :)

[1] https://lore.kernel.org/all/20251110204119.18351-1-zhiw@nvidia.com/