linux-kernel - Re: [PATCH 2/7] gpu: nova-core: Add support to convert bitfield to underlying type

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Message-ID: <bcea1756-d8db-442a-afed-ece32ba34aa9@nvidia.com>
Date: Mon, 20 Oct 2025 14:25:40 -0700
From: John Hubbard <jhubbard@...dia.com>
To: Joel Fernandes <joelagnelf@...dia.com>, linux-kernel@...r.kernel.org,
 rust-for-linux@...r.kernel.org, dri-devel@...ts.freedesktop.org,
 dakr@...nel.org, acourbot@...dia.com
Cc: 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,
 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,
 Elle Rhumsaa <elle@...thered-steel.dev>,
 Daniel Almeida <daniel.almeida@...labora.com>, nouveau@...ts.freedesktop.org
Subject: Re: [PATCH 2/7] gpu: nova-core: Add support to convert bitfield to
 underlying type

On 10/20/25 11:55 AM, Joel Fernandes wrote:
> To support the usecase where we read a register and write to another
> with identical bit layout, add support to convert bitfield to underlying type.
> 
> Another way to do this, is to read individual fields, on the caller
> side, and write to the destination fields, but that is both cumbersome
> and error-prone as new bits added in hardware may be missed.
> 
> Signed-off-by: Joel Fernandes <joelagnelf@...dia.com>
> ---
>  drivers/gpu/nova-core/bitfield.rs | 7 +++++++
>  1 file changed, 7 insertions(+)

Reviewed-by: John Hubbard <jhubbard@...dia.com>


thanks,
-- 
John Hubbard

> 
> diff --git a/drivers/gpu/nova-core/bitfield.rs b/drivers/gpu/nova-core/bitfield.rs
> index 0994505393dd..2266abc3f7ab 100644
> --- a/drivers/gpu/nova-core/bitfield.rs
> +++ b/drivers/gpu/nova-core/bitfield.rs
> @@ -72,6 +72,7 @@
>  /// - Field setters: `set_mode()`, `set_state()`, etc. (supports chaining with builder pattern).
>  ///   Note that the compiler will error out if the size of the setter's arg exceeds the
>  ///   struct's storage size.
> +/// - Conversion from the underlying storage type (e.g., `From<u32>`).
>  /// - Debug and Default implementations.
>  ///
>  /// Note: Field accessors and setters inherit the same visibility as the struct itself.
> @@ -117,6 +118,12 @@ fn from(val: $name) -> $storage {
>              }
>          }
>  
> +        impl ::core::convert::From<$storage> for $name {
> +            fn from(val: $storage) -> $name {
> +                $name(val)
> +            }
> +        }
> +
>          bitfield!(@fields_dispatcher $vis $name $storage { $($fields)* });
>      };
>