linux-kernel - Re: [PATCH v3 02/11] gpu: nova-core: move GSP boot code out of `Gpu` constructor

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Message-Id: <DCIKSL18GE9A.2R4BAGR56YVPF@kernel.org>
Date: Tue, 02 Sep 2025 21:53:12 +0200
From: "Danilo Krummrich" <dakr@...nel.org>
To: "Alexandre Courbot" <acourbot@...dia.com>
Cc: "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>, "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>, "John Hubbard"
 <jhubbard@...dia.com>, "Alistair Popple" <apopple@...dia.com>, "Joel
 Fernandes" <joelagnelf@...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 v3 02/11] gpu: nova-core: move GSP boot code out of
 `Gpu` constructor

On Tue Sep 2, 2025 at 4:31 PM CEST, Alexandre Courbot wrote:
> diff --git a/drivers/gpu/nova-core/driver.rs b/drivers/gpu/nova-core/driver.rs
> index 274989ea1fb4a5e3e6678a08920ddc76d2809ab2..1062014c0a488e959379f009c2e8029ffaa1e2f8 100644
> --- a/drivers/gpu/nova-core/driver.rs
> +++ b/drivers/gpu/nova-core/driver.rs
> @@ -6,6 +6,8 @@
>  
>  #[pin_data]
>  pub(crate) struct NovaCore {
> +    // Placeholder for the real `Gsp` object once it is built.
> +    pub(crate) gsp: (),
>      #[pin]
>      pub(crate) gpu: Gpu,
>      _reg: auxiliary::Registration,
> @@ -40,8 +42,14 @@ fn probe(pdev: &pci::Device<Core>, _info: &Self::IdInfo) -> Result<Pin<KBox<Self
>          )?;
>  
>          let this = KBox::pin_init(
> -            try_pin_init!(Self {
> +            try_pin_init!(&this in Self {
>                  gpu <- Gpu::new(pdev, bar)?,
> +                gsp <- {
> +                    // SAFETY: `this.gpu` is initialized to a valid value.
> +                    let gpu = unsafe { &(*this.as_ptr()).gpu };
> +
> +                    gpu.start_gsp(pdev)?
> +                },

Please use pin_chain() [1] for this.

More in general, unsafe code should be the absolute last resort. If we add new
unsafe code I'd love to see a comment justifying why there's no other way than
using unsafe code for this, as we agreed in [2].

I did a quick grep on this series and I see 21 occurrences of "unsafe", if I
substract the ones for annotations and for FromBytes impls, it's still 9 new
ones. :(

Do we really need all of them?

Otherwise, I really like this, it's a great improvement over initializing
everything into the Gpu struct -- thanks for the refactoring!

[1] https://rust.docs.kernel.org/kernel/prelude/trait.PinInit.html#method.pin_chain
[2] https://docs.kernel.org/gpu/nova/guidelines.html#language