linux-kernel - Re: [PATCH v2 1/4] rust: io: Add big-endian read and write functions

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Message-Id: <DG7E46M9VINC.3KTNQ1T7USPVO@kernel.org>
Date: Thu, 05 Feb 2026 23:43:48 +0100
From: "Danilo Krummrich" <dakr@...nel.org>
To: "Gary Guo" <gary@...yguo.net>
Cc: "Daniel Almeida" <daniel.almeida@...labora.com>, "Link Mauve"
 <linkmauve@...kmauve.fr>, <rust-for-linux@...r.kernel.org>, "Madhavan
 Srinivasan" <maddy@...ux.ibm.com>, "Michael Ellerman" <mpe@...erman.id.au>,
 "Nicholas Piggin" <npiggin@...il.com>, "Christophe Leroy (CS GROUP)"
 <chleroy@...nel.org>, "Srinivas Kandagatla" <srini@...nel.org>, "Miguel
 Ojeda" <ojeda@...nel.org>, "Boqun Feng" <boqun@...nel.org>,
 Björn Roy Baron <bjorn3_gh@...tonmail.com>, "Benno Lossin"
 <lossin@...nel.org>, "Andreas Hindborg" <a.hindborg@...nel.org>, "Alice
 Ryhl" <aliceryhl@...gle.com>, "Trevor Gross" <tmgross@...ch.edu>, "Ard
 Biesheuvel" <ardb@...nel.org>, "Martin K. Petersen"
 <martin.petersen@...cle.com>, "Eric Biggers" <ebiggers@...gle.com>, "Greg
 Kroah-Hartman" <gregkh@...uxfoundation.org>, "Lyude Paul"
 <lyude@...hat.com>, "Asahi Lina" <lina+kernel@...hilina.net>, "Viresh
 Kumar" <viresh.kumar@...aro.org>, "Lorenzo Stoakes"
 <lorenzo.stoakes@...cle.com>, "Tamir Duberstein" <tamird@...nel.org>,
 "FUJITA Tomonori" <fujita.tomonori@...il.com>,
 <linuxppc-dev@...ts.ozlabs.org>, <linux-kernel@...r.kernel.org>,
 <officialTechflashYT@...il.com>, "Ash Logan" <ash@...quark.com>, "Roberto
 Van Eeden" <rw-r-r-0644@...tonmail.com>,
 Jonathan Neuschäfer <j.neuschaefer@....net>
Subject: Re: [PATCH v2 1/4] rust: io: Add big-endian read and write
 functions

On Thu Feb 5, 2026 at 11:31 PM CET, Gary Guo wrote:
> On Thu Feb 5, 2026 at 7:05 PM GMT, Danilo Krummrich wrote:
>>   (1) Devices are either little-endian or big-endian. Hence, having to write
>>
>> 	io.big_endian().write()
>>
>>       is excessive, we always want big-endian for a big-endian device.
>
> You don't need to always write this. You just need to do `big_endian()` once
> when you obtain the io, and then keep using `BigEndian<Mmio>` instead of just
> `Mmio`, and the rest of code is still `.write()`.

<snip>

>>   (2) It is error prone, if you forget to call big_endian() first, it is a bug.
>
> Moot point when `big_endian()` is only done once.

Well, you need to do it at least once per driver entry point. For DRM IOCTLs for
instance you also have to consider that it is always Devres<Mmio>.