linux-kernel - Re: [PATCH 1/2] gpu: nova-core: vbios: split out PmuLookupTableHeader from PmuLookupTable

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Message-Id: <DBO9BTJ5Q8IM.2AY6DJQ9X9EIY@nvidia.com>
Date: Tue, 29 Jul 2025 13:34:08 +0900
From: "Alexandre Courbot" <acourbot@...dia.com>
To: "Rhys Lloyd" <krakow20@...il.com>, <dakr@...nel.org>
Cc: <rust-for-linux@...r.kernel.org>, <airlied@...il.com>,
 <simona@...ll.ch>, <nouveau@...ts.freedesktop.org>,
 <dri-devel@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] gpu: nova-core: vbios: split out
 PmuLookupTableHeader from PmuLookupTable

On Sun Jul 27, 2025 at 6:48 PM JST, Rhys Lloyd wrote:
> Separating the header allows the use of `size_of::<PmuLookupTableHeader>()`
> instead of the magic number 4.
>
> Signed-off-by: Rhys Lloyd <krakow20@...il.com>
> ---
>  drivers/gpu/nova-core/vbios.rs | 56 +++++++++++++++++++++-------------
>  1 file changed, 35 insertions(+), 21 deletions(-)
>
> diff --git a/drivers/gpu/nova-core/vbios.rs b/drivers/gpu/nova-core/vbios.rs
> index 5b5d9f38cbb3..a77d7a4c8595 100644
> --- a/drivers/gpu/nova-core/vbios.rs
> +++ b/drivers/gpu/nova-core/vbios.rs
> @@ -889,6 +889,32 @@ fn try_from(base: BiosImageBase) -> Result<Self> {
>      }
>  }
>  
> +/// The [`PmuLookupTableHeader`] structure is header information for [`PmuLookupTable`].
> +///
> +/// See the [`PmuLookupTable`] description for more information.
> +#[expect(dead_code)]
> +struct PmuLookupTableHeader {
> +    version: u8,
> +    header_len: u8,
> +    entry_len: u8,
> +    entry_count: u8,
> +}
> +
> +impl PmuLookupTableHeader {
> +    fn new(data: &[u8]) -> Result<Self> {
> +        if data.len() < core::mem::size_of::<Self>() {

We cannot rely on `size_of::<Self>` to be 4 if `Self` is not
`#[repr(C)]`. Since this is done in the second patch, I'd merge these
two into a single one for simplicity.