linux-kernel - Re: [PATCH v7.1 2/4] gpu: nova-core: bitfield: Move bitfield-specific code from register! into new macro

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Message-Id: <DDK92UVGWKGE.2LEEVWDBRGVMC@nvidia.com>
Date: Fri, 17 Oct 2025 11:43:42 +0900
From: "Alexandre Courbot" <acourbot@...dia.com>
To: "John Hubbard" <jhubbard@...dia.com>, "Danilo Krummrich"
 <dakr@...nel.org>, "Joel Fernandes" <joelagnelf@...dia.com>
Cc: "Yury Norov" <yury.norov@...il.com>, "linux-kernel@...r.kernel.org"
 <linux-kernel@...r.kernel.org>, "rust-for-linux@...r.kernel.org"
 <rust-for-linux@...r.kernel.org>, "dri-devel@...ts.freedesktop.org"
 <dri-devel@...ts.freedesktop.org>, "Alexandre Courbot"
 <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" <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>, "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>, "Timur
 Tabi" <ttabi@...dia.com>, "joel@...lfernandes.org"
 <joel@...lfernandes.org>, "Elle Rhumsaa" <elle@...thered-steel.dev>,
 "Daniel Almeida" <daniel.almeida@...labora.com>,
 "nouveau@...ts.freedesktop.org" <nouveau@...ts.freedesktop.org>, "Edwin
 Peer" <epeer@...dia.com>
Subject: Re: [PATCH v7.1 2/4] gpu: nova-core: bitfield: Move
 bitfield-specific code from register! into new macro

On Fri Oct 17, 2025 at 4:39 AM JST, John Hubbard wrote:
> On 10/16/25 12:34 PM, Danilo Krummrich wrote:
>> On Thu Oct 16, 2025 at 9:28 PM CEST, Joel Fernandes wrote:
>>>> On Oct 16, 2025, at 1:48 PM, Yury Norov <yury.norov@...il.com> wrote:
>>>> On Thu, Oct 16, 2025 at 11:13:21AM -0400, Joel Fernandes wrote:
> ...
>> While I'm not super opinionated for general bitfields, for the register!()
>> infrastructure I very much prefer the hi:lo notation, as this is the common
>> notation in datasheets and TRMs.
>> 
>> However, if we use hi:lo, we should use it decending, i.e.:
>> 
>
> Sure, descending works.
>
>> 	bitfield! {
>> 	    struct ControlReg {
>> 	        7:5 state as u8 => State;
>> 	        3:0 mode as u8 ?=> Mode;
>
> And hi:lo matches our HW reference manuals. And if you're dealing
> with bitfields, you are often also dealing with HW, so this is
> a reasonable place in the SW to use hi:lo.

Definitely agree here. The use of `:` is what makes the difference with
the GENMASK macro, which separates its argument with a regular comma.
There is no room for mistaking these with anything else.