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

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Message-Id: <DBD3I0RWQ39M.XA1Q0WSOJWSE@nvidia.com>
Date: Wed, 16 Jul 2025 10:40:47 +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] gpu: nova-core: vbios: split out PmuLookupTableHeader
 from PmuLookupTable

On Mon Jul 14, 2025 at 7:43 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 663fc50e8b66..20011c5c9bbc 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 {

Can you add a 

  // TODO[TRSM]: use FromBytes::from_bytes when it becomes available.

as ultimately that's what we want to do.

(we are using these markers to keep track of tasks to complete as Rust
features land, see Documentation/gpu/nova/core/todo.rst)

> +    fn new(data: &[u8]) -> Result<Self> {
> +        if data.len() < core::mem::size_of::<Self>() {
> +            return Err(EINVAL);
> +        }
> +
> +        Ok(PmuLookupTableHeader {
> +            version: data[0],

How about making `PmuLookupTableHeader` `#[repr(C)]` and using
`offset_of!`? This will also set the stage for the transition to using
`FromBytes::from_bytes`.