linux-kernel - Re: [PATCH] gpu: nova-core: bitfield: use &mut self setters instead of builder pattern

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Message-ID: <9db27bd6015ccebaa20e51450d8c42eb2864cb2e.camel@nvidia.com>
Date: Wed, 31 Dec 2025 22:33:41 +0000
From: Timur Tabi <ttabi@...dia.com>
To: "dakr@...nel.org" <dakr@...nel.org>, John Hubbard <jhubbard@...dia.com>
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Subject: Re: [PATCH] gpu: nova-core: bitfield: use &mut self setters instead
 of builder pattern

On Wed, 2025-12-31 at 13:47 -0800, John Hubbard wrote:
> The builder-pattern setters (self -> Self) enabled method chaining like:
> 
>     reg.set_foo(x).set_sec(y).write(bar);
> 
> This made separate operations appear as a single expression, obscuring
> that each setter is a distinct mutation. 

So you're concerned about the fact that the compiler is not merging the set_foo(x) and the
set_sec(y) into a single read-modify-write?

> These setters are infallible,
> so the chaining provides no error-propagation benefit—it just obscures
> what are simple, independent assignments.
> 
> Change the bitfield!() macro to generate `&mut self` setters, so each
> operation is a distinct statement:
> 
>     reg.set_foo(x);
>     reg.set_sec(y);
>     reg.write(bar);

Are you sure about this?  It just seems like you're throwing out a neat little feature of Rust and
replacing it with something that's very C-like.  This breaks compatible with all users of the regs
macros.  Seems really disruptive for what seems to me like a cosmetic change.