[PATCH v2 19/19] gpu: nova-core: firmware: parse `FalconUCodeDescV2` via `zerocopy`

Now that we have `zerocopy` support, we can avoid some `unsafe` code.

For instance, for `FalconUCodeDescV2`, we can replace the `unsafe impl
FromBytes` by safely deriving `zerocopy`'s `FromBytes` and then calling
`read_from_prefix`.

Reviewed-by: Alexandre Courbot <[email protected]>
Acked-by: Danilo Krummrich <[email protected]>
Signed-off-by: Miguel Ojeda <[email protected]>
---
 drivers/gpu/nova-core/firmware.rs | 5 +----
 drivers/gpu/nova-core/vbios.rs    | 6 ++++--
 2 files changed, 5 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/nova-core/firmware.rs b/drivers/gpu/nova-core/firmware.rs
index 6c2ab69cb605..ad37994ac15a 100644
--- a/drivers/gpu/nova-core/firmware.rs
+++ b/drivers/gpu/nova-core/firmware.rs
@@ -48,7 +48,7 @@ fn request_firmware(
 
 /// Structure used to describe some firmwares, notably FWSEC-FRTS.
 #[repr(C)]
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, FromBytes)]
 pub(crate) struct FalconUCodeDescV2 {
     /// Header defined by 'NV_BIT_FALCON_UCODE_DESC_HEADER_VDESC*' in OpenRM.
     hdr: u32,
@@ -84,9 +84,6 @@ pub(crate) struct FalconUCodeDescV2 {
     pub(crate) alt_dmem_load_size: u32,
 }
 
-// SAFETY: all bit patterns are valid for this type, and it doesn't use interior mutability.
-unsafe impl FromBytes for FalconUCodeDescV2 {}
-
 /// Structure used to describe some firmwares, notably FWSEC-FRTS.
 #[repr(C)]
 #[derive(Debug, Clone)]
diff --git a/drivers/gpu/nova-core/vbios.rs b/drivers/gpu/nova-core/vbios.rs
index ebda28e596c5..8b7d17a24660 100644
--- a/drivers/gpu/nova-core/vbios.rs
+++ b/drivers/gpu/nova-core/vbios.rs
@@ -16,6 +16,8 @@
     transmute::FromBytes,
 };
 
+use zerocopy::FromBytes as _;
+
 use crate::{
     driver::Bar0,
     firmware::{
@@ -1011,8 +1013,8 @@ pub(crate) fn header(&self) -> Result<FalconUCodeDesc> {
         let data = self.base.data.get(falcon_ucode_offset..).ok_or(EINVAL)?;
         match ver {
             2 => {
-                let v2 = FalconUCodeDescV2::from_bytes_copy_prefix(data)
-                    .ok_or(EINVAL)?
+                let v2 = FalconUCodeDescV2::read_from_prefix(data)
+                    .map_err(|_| EINVAL)?
                     .0;
                 Ok(FalconUCodeDesc::V2(v2))
             }
-- 
2.54.0