linux-kernel - Re: [PATCH v2 3/7] gpu: nova-core: vbios: add conversion to u8 for BiosImageType

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Message-Id: <DDTRWUSQDWJC.1UPRDDOSLXN5F@nvidia.com>
Date: Tue, 28 Oct 2025 16:23:13 +0900
From: "Alexandre Courbot" <acourbot@...dia.com>
To: "Joel Fernandes" <joelagnelf@...dia.com>
Cc: "Alice Ryhl" <aliceryhl@...gle.com>, "David Airlie" <airlied@...il.com>,
 "Simona Vetter" <simona@...ll.ch>, "Miguel Ojeda" <ojeda@...nel.org>, "Alex
 Gaynor" <alex.gaynor@...il.com>, "Boqun Feng" <boqun.feng@...il.com>, "Gary
 Guo" <gary@...yguo.net>, Björn Roy Baron
 <bjorn3_gh@...tonmail.com>, "Benno Lossin" <lossin@...nel.org>, "Andreas
 Hindborg" <a.hindborg@...nel.org>, "Trevor Gross" <tmgross@...ch.edu>,
 "John Hubbard" <jhubbard@...dia.com>, "Alistair Popple"
 <apopple@...dia.com>, "Timur Tabi" <ttabi@...dia.com>, "Edwin Peer"
 <epeer@...dia.com>, <nouveau@...ts.freedesktop.org>,
 <dri-devel@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>,
 <rust-for-linux@...r.kernel.org>, "Danilo Krummrich" <dakr@...nel.org>,
 "Nouveau" <nouveau-bounces@...ts.freedesktop.org>
Subject: Re: [PATCH v2 3/7] gpu: nova-core: vbios: add conversion to u8 for
 BiosImageType

On Tue Oct 28, 2025 at 2:37 AM JST, Joel Fernandes wrote:
> Hello Alex,
>
> On Mon, Oct 27, 2025 at 09:54:43PM +0900, Alexandre Courbot wrote:
>> Since `BiosImageType` is `repr(u8)`, if can safely be converted into a
>> `u8` but this is not obvious when doing this in the code.
>> 
>> Instead, implement `From<BiosImageType>` for `u8` so the cast can be
>> done in a single place, with a justifying comment.
>> 
>> Acked-by: Danilo Krummrich <dakr@...nel.org>
>> Signed-off-by: Alexandre Courbot <acourbot@...dia.com>
>> ---
>>  drivers/gpu/nova-core/vbios.rs | 9 ++++++++-
>>  1 file changed, 8 insertions(+), 1 deletion(-)
>> 
>> diff --git a/drivers/gpu/nova-core/vbios.rs b/drivers/gpu/nova-core/vbios.rs
>> index dbe0d6e4a015..a521c0a4df0f 100644
>> --- a/drivers/gpu/nova-core/vbios.rs
>> +++ b/drivers/gpu/nova-core/vbios.rs
>> @@ -50,6 +50,13 @@ fn try_from(code: u8) -> Result<Self> {
>>      }
>>  }
>>  
>> +impl From<BiosImageType> for u8 {
>> +    fn from(value: BiosImageType) -> Self {
>> +        // `BiosImageType` is `repr(u8)` and thus convertible without loss.
>> +        value as u8
>> +    }
>> +}
>> +
>>  // PMU lookup table entry types. Used to locate PMU table entries
>>  // in the Fwsec image, corresponding to falcon ucodes.
>>  #[expect(dead_code)]
>> @@ -711,7 +718,7 @@ fn image_type(&self) -> Result<BiosImageType> {
>>      fn is_last(&self) -> bool {
>>          // For NBSI images (type == 0x70), return true as they're
>>          // considered the last image
>> -        if self.pcir.code_type == BiosImageType::Nbsi as u8 {
>> +        if self.pcir.code_type == BiosImageType::Nbsi.into() {
>
> I strongly prefer u8::from(BiosImageType::Nbsi) here so there is no loss of
> readability of the type. Can we please use ::from()?

What benefit do we get from knowing the representing type of
BiosImageType? We are only interested in knowing whether the two values
are equal or not.

But you have a point that `::from()` is generally easier to read, only I
would apply it on the left value:

  if BiosImageType::try_from(self.pcir.code_type) == Ok(BiosImageType::Nbsi)

or reusing the already existing code:

  if self.image_type() == Ok(BiosImageType::Nbsi)

That reads even more naturally imho.