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

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Message-Id: <20251020185539.49986-3-joelagnelf@nvidia.com>
Date: Mon, 20 Oct 2025 14:55:34 -0400
From: Joel Fernandes <joelagnelf@...dia.com>
To: 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>,
	John Hubbard <jhubbard@...dia.com>,
	Joel Fernandes <joelagnelf@...dia.com>,
	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: [PATCH 2/7] gpu: nova-core: Add support to convert bitfield to underlying type

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(+)

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)* });
     };
 
-- 
2.34.1