Re: [PATCH v2 3/5] drm/nova: use `zerocopy` in fwsec.rs

[Alistair Popple <apopple@nvidia.com>]

On 2026-07-02 at 22:03 +1000, Pedro Yudi Honda <niyudi.honda@usp.br> wrote...
> From: Pedro Yudi Honda <niyudi.honda@usp.br>
> 
> In firmware/fwsec.rs, replace the following `transmute` traits with
> their `zerocopy` equivalents:
> 
> - `transmute::FromBytes` -> `zerocopy::FromBytes`
> - `transmute::AsBytes` -> `zerocopy::IntoBytes`
> - add `zerocopy::KnownLayout` where necessary

Argh, ok. It makes more sense when there are more things in the list :-) That
said I'd also be ok without, but either is fine.

Reviewed-by: Alistair Popple <apopple@nvidia.com>

> Update call sites accordingly.
> 
> Signed-off-by: Pedro Yudi Honda <niyudi.honda@usp.br>
> ---
>  drivers/gpu/nova-core/firmware/fwsec.rs | 49 ++++++-------------------
>  1 file changed, 12 insertions(+), 37 deletions(-)
> 
> diff --git a/drivers/gpu/nova-core/firmware/fwsec.rs b/drivers/gpu/nova-core/firmware/fwsec.rs
> index 95e0dd77746b..1b75cdc02256 100644
> --- a/drivers/gpu/nova-core/firmware/fwsec.rs
> +++ b/drivers/gpu/nova-core/firmware/fwsec.rs
> @@ -19,11 +19,7 @@
>          self,
>          Device, //
>      },
> -    prelude::*,
> -    transmute::{
> -        AsBytes,
> -        FromBytes, //
> -    },
> +    prelude::*, //
>  };
>  
>  use crate::{
> @@ -49,26 +45,22 @@
>  const NVFW_FALCON_APPIF_ID_DMEMMAPPER: u32 = 0x4;
>  
>  #[repr(C)]
> -#[derive(Debug)]
> +#[derive(Debug, FromBytes)]
>  struct FalconAppifHdrV1 {
>      version: u8,
>      header_size: u8,
>      entry_size: u8,
>      entry_count: u8,
>  }
> -// SAFETY: Any byte sequence is valid for this struct.
> -unsafe impl FromBytes for FalconAppifHdrV1 {}
>  
>  #[repr(C, packed)]
> -#[derive(Debug)]
> +#[derive(Debug, FromBytes)]
>  struct FalconAppifV1 {
>      id: u32,
>      dmem_base: u32,
>  }
> -// SAFETY: Any byte sequence is valid for this struct.
> -unsafe impl FromBytes for FalconAppifV1 {}
>  
> -#[derive(Debug)]
> +#[derive(Debug, FromBytes, IntoBytes, zerocopy_derive::KnownLayout)]
>  #[repr(C, packed)]
>  struct FalconAppifDmemmapperV3 {
>      signature: u32,
> @@ -89,12 +81,8 @@ struct FalconAppifDmemmapperV3 {
>      ucode_cmd_mask1: u32,
>      multi_tgt_tbl: u32,
>  }
> -// SAFETY: Any byte sequence is valid for this struct.
> -unsafe impl FromBytes for FalconAppifDmemmapperV3 {}
> -// SAFETY: This struct doesn't contain uninitialized bytes and doesn't have interior mutability.
> -unsafe impl AsBytes for FalconAppifDmemmapperV3 {}
>  
> -#[derive(Debug)]
> +#[derive(Debug, FromBytes, IntoBytes, zerocopy_derive::KnownLayout)]
>  #[repr(C, packed)]
>  struct ReadVbios {
>      ver: u32,
> @@ -103,12 +91,8 @@ struct ReadVbios {
>      size: u32,
>      flags: u32,
>  }
> -// SAFETY: Any byte sequence is valid for this struct.
> -unsafe impl FromBytes for ReadVbios {}
> -// SAFETY: This struct doesn't contain uninitialized bytes and doesn't have interior mutability.
> -unsafe impl AsBytes for ReadVbios {}
>  
> -#[derive(Debug)]
> +#[derive(Debug, FromBytes, IntoBytes, zerocopy_derive::KnownLayout)]
>  #[repr(C, packed)]
>  struct FrtsRegion {
>      ver: u32,
> @@ -117,22 +101,15 @@ struct FrtsRegion {
>      size: u32,
>      ftype: u32,
>  }
> -// SAFETY: Any byte sequence is valid for this struct.
> -unsafe impl FromBytes for FrtsRegion {}
> -// SAFETY: This struct doesn't contain uninitialized bytes and doesn't have interior mutability.
> -unsafe impl AsBytes for FrtsRegion {}
>  
>  const NVFW_FRTS_CMD_REGION_TYPE_FB: u32 = 2;
>  
>  #[repr(C, packed)]
> +#[derive(FromBytes, IntoBytes, zerocopy_derive::KnownLayout)]
>  struct FrtsCmd {
>      read_vbios: ReadVbios,
>      frts_region: FrtsRegion,
>  }
> -// SAFETY: Any byte sequence is valid for this struct.
> -unsafe impl FromBytes for FrtsCmd {}
> -// SAFETY: This struct doesn't contain uninitialized bytes and doesn't have interior mutability.
> -unsafe impl AsBytes for FrtsCmd {}
>  
>  const NVFW_FALCON_APPIF_DMEMMAPPER_CMD_FRTS: u32 = 0x15;
>  const NVFW_FALCON_APPIF_DMEMMAPPER_CMD_SB: u32 = 0x19;
> @@ -151,11 +128,9 @@ pub(crate) enum FwsecCommand {
>  
>  /// A single signature that can be patched into a FWSEC image.
>  #[repr(transparent)]
> +#[derive(FromBytes)]
>  pub(crate) struct Bcrt30Rsa3kSignature([u8; BCRT30_RSA3K_SIG_SIZE]);
>  
> -/// SAFETY: A signature is just an array of bytes.
> -unsafe impl FromBytes for Bcrt30Rsa3kSignature {}
> -
>  impl From<[u8; BCRT30_RSA3K_SIG_SIZE]> for Bcrt30Rsa3kSignature {
>      fn from(sig: [u8; BCRT30_RSA3K_SIG_SIZE]) -> Self {
>          Self(sig)
> @@ -228,7 +203,7 @@ fn new_fwsec(bios: &Vbios, cmd: FwsecCommand) -> Result<Self> {
>  
>          let hdr = ucode
>              .get(hdr_offset..)
> -            .and_then(FalconAppifHdrV1::from_bytes_prefix)
> +            .and_then(|b| FalconAppifHdrV1::read_from_prefix(b).ok())
>              .ok_or(EINVAL)?
>              .0;
>  
> @@ -246,7 +221,7 @@ fn new_fwsec(bios: &Vbios, cmd: FwsecCommand) -> Result<Self> {
>  
>              let app = ucode
>                  .get(entry_offset..)
> -                .and_then(FalconAppifV1::from_bytes_prefix)
> +                .and_then(|b| FalconAppifV1::read_from_prefix(b).ok())
>                  .ok_or(EINVAL)?
>                  .0;
>  
> @@ -263,7 +238,7 @@ fn new_fwsec(bios: &Vbios, cmd: FwsecCommand) -> Result<Self> {
>  
>              let dmem_mapper = ucode
>                  .get_mut(dmem_mapper_offset..)
> -                .and_then(FalconAppifDmemmapperV3::from_bytes_mut_prefix)
> +                .and_then(|b| FalconAppifDmemmapperV3::mut_from_prefix(b).ok())
>                  .ok_or(EINVAL)?
>                  .0;
>  
> @@ -281,7 +256,7 @@ fn new_fwsec(bios: &Vbios, cmd: FwsecCommand) -> Result<Self> {
>  
>              let frts_cmd = ucode
>                  .get_mut(frts_cmd_offset..)
> -                .and_then(FrtsCmd::from_bytes_mut_prefix)
> +                .and_then(|b| FrtsCmd::mut_from_prefix(b).ok())
>                  .ok_or(EINVAL)?
>                  .0;
>  
> -- 
> 2.34.1
>