Message-Id: <DCSLPCSQRYOY.3BX3008H5CVQP@kernel.org>
Date: Sun, 14 Sep 2025 16:42:40 +0200
From: "Benno Lossin" <lossin@...nel.org>
To: "Alexandre Courbot" <acourbot@...dia.com>, "Joel Fernandes"
 <joelagnelf@...dia.com>, "John Hubbard" <jhubbard@...dia.com>
Cc: "Miguel Ojeda" <miguel.ojeda.sandonis@...il.com>, "Danilo Krummrich"
 <dakr@...nel.org>, "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>, "Andreas Hindborg" <a.hindborg@...nel.org>,
 "Alice Ryhl" <aliceryhl@...gle.com>, "Trevor Gross" <tmgross@...ch.edu>,
 "David Airlie" <airlied@...il.com>, "Simona Vetter" <simona@...ll.ch>,
 "Maarten Lankhorst" <maarten.lankhorst@...ux.intel.com>, "Maxime Ripard"
 <mripard@...nel.org>, "Thomas Zimmermann" <tzimmermann@...e.de>, "Alistair
 Popple" <apopple@...dia.com>, "Timur Tabi" <ttabi@...dia.com>,
 <rust-for-linux@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
 <nouveau@...ts.freedesktop.org>, <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH v5 02/12] gpu: nova-core: move GSP boot code to a
 dedicated method

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

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