Nouveau - Oct 2025 - [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 at nvidia.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

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 at nvidia.com>
> ---
>  drivers/gpu/nova-core/bitfield.rs | 7 +++++++
>  1 file changed, 7 insertions(+)
Reviewed-by: John Hubbard <jhubbard at nvidia.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)* });
>      };
>

On Tue Oct 21, 2025 at 3:55 AM JST, 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.
Shouldn't the title be "Add support to convert bitfield FROM underlying
type"? Since this adds a `From<storage> for Bitfield`.