Nouveau - Sep 2025 - [PATCH v5 02/12] gpu: nova-core: move GSP boot code to a dedicated method

On Sun Sep 14, 2025 at 7:06 AM JST, Joel Fernandes
wrote:
> On Sat, Sep 13, 2025 at 02:29:54PM -0700, John Hubbard wrote:
> [..]
>
>> > 
>> > I would suggest taking a look at our website and the links there
(like
>> > issue #2) -- what we are doing upstream Rust is documented.
>> 
>> ...and my question was asked before reading through issue #2. So your
>> and Danilo's responses seem to be saying that there is already some
>> understanding that this is an area that could be improved.
>> 
>> Good!
>> 
>> I believe "issue #2" refers to this, right?
>> 
>>    https://github.com/Rust-for-Linux/linux/issues/2
>> 
>> That's going to take some time to figure out if it interects
>> what I was requesting, but I'll have a go at it.
>
> Indeed, kudos to rust-for-linux community for working on missing Rust
> features and on pinning itself.
>
>> > 
>> > (Danilo gave you a direct link, but I mention it this way because
>> > there are a lot of things going on, and it is worth a look and
perhaps
>> > you may find something interesting you could help with).
>> > 
>> > > except to satisfy paranoia
>> > 
>> > Using unsafe code everywhere (or introducing unsoundness or UB for
>> > convenience) would defeat much of the Rust for Linux exercise.
>> > 
>> 
>> Yes. It's only "paranoia" if the code is bug-free. So
Rust itself
>> naturally will look "a little" paranoid, that's core to
its mission. :)
>
> This seems to be taken out-of-context, I said "paranoia" mainly
because I am
> not sure if excessive use of pinning may tend to cause other problems. The
> "paranoia" is about over-usage of pinning. Personally, I
don't prefer to pin
> stuff in my code until I absolutely need to, or when I start having needs
for
> pinning, like using spinlocks. Maybe I am wrong, but the way I learnt Rust,
> data movement is baked into it. I am not yet confident pinning will not
> constraint Rust code gen -- but that could just be a part of my learning
> journey that I have to convince myself it is Ok to do so in advance of
> actually requiring it even if you simply hypothetically anticipate needing
it
> (as Danilo pointed out that in practice this is not an issue and I do tend
to
> agree with Miguel and Danilo because they are usually right :-D). I am
> researching counter examples :-)
You can look at the definition for `Pin` in [1], but it is so short we
can paste it here:

    #[repr(transparent)]
    #[derive(Copy, Clone)]
    pub struct Pin<Ptr> {
        pointer: Ptr,
    }

There isn't much getting in the way of optimized code generation - its
purpose is simply to constraint the acquisition of mutable references to
prevent moving the pointee out.

I started this patchset a little bit skeptical about the need to pin so
many things, but after seeing the recent additions to `pin_init` and
rewriting the code as Danilo suggested, it starteds to click. The
supposed restrictions are in practice avoided by embracing the concept
fully, and in the end I got that feeling (familiar when writing Rust) of
being guided towards the right design - a bit like playing bowling with
gutter guards.

Yes, that means redesigning and rebasing our code, but that's also the
cost of learning a new language.

And yes, things can still be a little bit rough around the edges, but
there is awareness and action taken to address these issues, at the
compiler level when relevant. This makes me confident for the future.

[1] https://doc.rust-lang.org/src/core/pin.rs.html#1094

On Sun Sep 14, 2025 at 3:49 AM CEST, Alexandre Courbot
wrote:
> On Sun Sep 14, 2025 at 7:06 AM JST, Joel Fernandes wrote:
>> On Sat, Sep 13, 2025 at 02:29:54PM -0700, John Hubbard wrote:
>>> Yes. It's only "paranoia" if the code is bug-free. So
Rust itself
>>> naturally will look "a little" paranoid, that's core
to its mission. :)
>>
>> This seems to be taken out-of-context, I said "paranoia"
mainly because I am
>> not sure if excessive use of pinning may tend to cause other problems.
The
>> "paranoia" is about over-usage of pinning. Personally, I
don't prefer to pin
>> stuff in my code until I absolutely need to, or when I start having
needs for
>> pinning, like using spinlocks. Maybe I am wrong, but the way I learnt
Rust,
>> data movement is baked into it. I am not yet confident pinning will not
>> constraint Rust code gen -- but that could just be a part of my
learning
>> journey that I have to convince myself it is Ok to do so in advance of
>> actually requiring it even if you simply hypothetically anticipate
needing it
>> (as Danilo pointed out that in practice this is not an issue and I do
tend to
>> agree with Miguel and Danilo because they are usually right :-D). I am
>> researching counter examples :-)
>
> You can look at the definition for `Pin` in [1], but it is so short we
> can paste it here:
>
>     #[repr(transparent)]
>     #[derive(Copy, Clone)]
>     pub struct Pin<Ptr> {
>         pointer: Ptr,
>     }
>
> There isn't much getting in the way of optimized code generation - its
> purpose is simply to constraint the acquisition of mutable references to
> prevent moving the pointee out.
>
> I started this patchset a little bit skeptical about the need to pin so
> many things, but after seeing the recent additions to `pin_init` and
> rewriting the code as Danilo suggested, it starteds to click. The
> supposed restrictions are in practice avoided by embracing the concept
> fully, and in the end I got that feeling (familiar when writing Rust) of
> being guided towards the right design - a bit like playing bowling with
> gutter guards.
That's a great way to put it -- I had a similar experience when writing
pin-init and thinking about it purely theoretically. Good to see that it
works out in practice (and continues to do so :).
> Yes, that means redesigning and rebasing our code, but that's also the
> cost of learning a new language.
>
> And yes, things can still be a little bit rough around the edges, but
> there is awareness and action taken to address these issues, at the
> compiler level when relevant. This makes me confident for the future.
If you have an issue that you cannot work around, or something that
looks off, let me know. Maybe that's something that pin-init can deal
better with or we can have another library that helps with it. After all
pin-init is specially tailored for the kernel to work :)

---
Cheers,
Benno