gpu: nova-core: make Architecture behave as a u8 type

This allows Architecture to be passed into register!() and bitfield!()
macro calls. That in turn requires a default implementation for
Architecture.

This simplifies transforming BOOT0 (and later, BOOT42) register values
into GPU architectures.

Cc: Danilo Krummrich <dakr@kernel.org>
Cc: Timur Tabi <ttabi@nvidia.com>
Suggested-by: Alexandre Courbot <acourbot@nvidia.com>
Reviewed-by: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Message-ID: <20251115010923.1192144-3-jhubbard@nvidia.com>

drivers/gpu/nova-core/gpu.rs

@@ -122,8 +122,14 @@ impl fmt::Display for Chipset {
 }
 
 /// Enum representation of the GPU generation.
-#[derive(fmt::Debug)]
+///
+/// TODO: remove the `Default` trait implementation, and the `#[default]`
+/// attribute, once the register!() macro (which creates Architecture items) no
+/// longer requires it for read-only fields.
+#[derive(fmt::Debug, Default, Copy, Clone)]
+#[repr(u8)]
 pub(crate) enum Architecture {
+    #[default]
     Turing = 0x16,
     Ampere = 0x17,
     Ada = 0x19,
@@ -142,6 +148,13 @@ impl TryFrom<u8> for Architecture {
     }
 }
 
+impl From<Architecture> for u8 {
+    fn from(value: Architecture) -> Self {
+        // CAST: `Architecture` is `repr(u8)`, so this cast is always lossless.
+        value as u8
+    }
+}
+
 pub(crate) struct Revision {
     major: u8,
     minor: u8,