linux-kernel - Re: [PATCH v4 1/6] nova-core: bitfield: Move bitfield-specific code from register! into new macro

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Message-Id: <DD5KED38XJS7.3DIP0BEWMD1XV@kernel.org>
Date: Mon, 29 Sep 2025 22:25:57 +0200
From: "Danilo Krummrich" <dakr@...nel.org>
To: "Joel Fernandes" <joelagnelf@...dia.com>
Cc: "Greg KH" <gregkh@...uxfoundation.org>, "Benno Lossin"
 <lossin@...nel.org>, <linux-kernel@...r.kernel.org>,
 <rust-for-linux@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
 <acourbot@...dia.com>, "Alistair Popple" <apopple@...dia.com>, "Miguel
 Ojeda" <ojeda@...nel.org>, "Alex Gaynor" <alex.gaynor@...il.com>, "Boqun
 Feng" <boqun.feng@...il.com>, "Gary Guo" <gary@...yguo.net>,
 <bjorn3_gh@...tonmail.com>, "Andreas Hindborg" <a.hindborg@...nel.org>,
 "Alice Ryhl" <aliceryhl@...gle.com>, "Trevor Gross" <tmgross@...ch.edu>,
 "David Airlie" <airlied@...il.com>, "Simona Vetter" <simona@...ll.ch>,
 "Maarten Lankhorst" <maarten.lankhorst@...ux.intel.com>, "Maxime Ripard"
 <mripard@...nel.org>, "Thomas Zimmermann" <tzimmermann@...e.de>, "John
 Hubbard" <jhubbard@...dia.com>, "Timur Tabi" <ttabi@...dia.com>,
 <joel@...lfernandes.org>, "Elle Rhumsaa" <elle@...thered-steel.dev>, "Yury
 Norov" <yury.norov@...il.com>, "Daniel Almeida"
 <daniel.almeida@...labora.com>, <nouveau@...ts.freedesktop.org>
Subject: Re: [PATCH v4 1/6] nova-core: bitfield: Move bitfield-specific code
 from register! into new macro

On Mon Sep 29, 2025 at 9:26 PM CEST, Joel Fernandes wrote:
> On 9/24/2025 12:40 PM, Greg KH wrote:
>> On Tue, Sep 23, 2025 at 06:24:34PM -0400, Joel Fernandes wrote:
> [..]
>> 
>>> For the separate issue of enforcing endianness with respect to (across)
>>> multiple fields, I agree with you that if the user's backend (the consumer of
>>> the data) is not doing such conversion, say via regmap, then that becomes a
>>> problem. But that problem is orthogonal/different and cannot be solved here.  
>> 
>> But that is exactly what these macros are being defined here for, so to
>> ignore that is going to cause problems :)
>> 
>
> If needed, happy to add endianness support as needed by providing additional
> options to the macro. Based on this thread, it sounds like we want see if that
> is really needed here or can be solved elsewhere (?). The mental model I kind of
> have is this macro should only be dealing with CPU native endianness, much like
> bitfields in C deal with CPU endianness. Hmm.

At least for register!() we don't need anything else than CPU endianness. In
fact, as described in [1], any representation is fine as long as it is
consistent.

[1] https://lore.kernel.org/all/DD0ZTZM8S84H.1YDWSY7DF14LM@kernel.org/