Nouveau - Aug 2025 - [PATCH v6 2/5] rust: pci: provide access to PCI Vendor values

On 8/26/25 10:38 PM, John Hubbard wrote:
> On 8/25/25 5:47 AM, Danilo Krummrich wrote:
>> On Mon Aug 25, 2025 at 2:33 PM CEST, Alexandre Courbot wrote:
> ...
>>> Naive question from someone with a device tree background and
almost no
>>> PCI experience: one consequence of using `From` here is that if I
create
>>> an non-registered Vendor value (e.g. `let vendor >>>
Vendor::from(0xf0f0)`), then do `vendor.as_raw()`, I won't get the value
>>> passed initially but the one for `UNKNOWN`, e.g. `0xffff`. Are we
ok
>>> with this?
>>
>> I think that's fine, since we shouldn't actually hit this.
Drivers should only
>> ever use the pre-defined constants of Vendor; consequently the
>> Device::vendor_id() can't return UNKNOWN either.
>>
>> So, I think the From impl is not ideal, since we can't limit its
visibility. In
>> order to improve this, I suggest to use Vendor::new() directly in the
macro, and
>> make Vendor::new() private. The same goes for Class, I guess.
> 
> Correction: when I went to implement this, I discovered that there is a
better
> way, which addresses both Alex's and your concerns.
> 
> The incremental diff below shows how. It provides:
> 
> a) .from_raw(), which in this case matches conventions slightly better
>     than new(). (I'm still learning that the Rust way is a bit
different
>     that the C++ way! haha).
> 
> b) Only the parent module (in this case, that's pci:: ) can call
>     Class::from_raw(). This is exactly what we need. Fully private methods
>     wouldn't work, but leaving it open for any caller to construct a
>     Class item is also a problem.
Sorry, that's on me being not precise. When I said private I meant private
to
the parent module.

The diff looks good, thanks!

Please also make sure to add #[inline] where appropriate and rebase onto
driver-core-next.

On 8/26/25 1:45 PM, Danilo Krummrich wrote:
> On 8/26/25 10:38 PM, John Hubbard wrote:
>> On 8/25/25 5:47 AM, Danilo Krummrich wrote:
>>> On Mon Aug 25, 2025 at 2:33 PM CEST, Alexandre Courbot wrote:
>> ...
> Sorry, that's on me being not precise. When I said private I meant
private to
> the parent module.
> 
> The diff looks good, thanks!
Huge relief! :)
> 
> Please also make sure to add #[inline] where appropriate and rebase onto
> driver-core-next.
I have no idea "where appropriate" is, here. These are not hot paths,
and
the existing pci.rs methods such as Device::vendor_id() are not inlined,
and so my initial approach is to just not inline any of this...

thanks,
-- 
John Hubbard