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

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Message-Id: <DCJ3R8YQUYK1.3K5BCWHMAEOL7@nvidia.com>
Date: Wed, 03 Sep 2025 19:44:49 +0900
From: "Alexandre Courbot" <acourbot@...dia.com>
To: "Danilo Krummrich" <dakr@...nel.org>
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 Wed Sep 3, 2025 at 5:26 PM JST, Danilo Krummrich wrote:
> On Wed Sep 3, 2025 at 9:08 AM CEST, Alexandre Courbot wrote:
>> On Wed Sep 3, 2025 at 4:53 AM JST, Danilo Krummrich wrote:
>>> 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.
>>
>> Sorry, but I couldn't figure out how I can use pin_chain here (and
>> couldn't find any relevant example in the kernel code either). Can you
>> elaborate a bit?
>
> I thought of just doing the following, which I think should be equivalent (diff
> against current nova-next).
>
> diff --git a/drivers/gpu/nova-core/driver.rs b/drivers/gpu/nova-core/driver.rs
> index 274989ea1fb4..6d62867f7503 100644
> --- a/drivers/gpu/nova-core/driver.rs
> +++ b/drivers/gpu/nova-core/driver.rs
> @@ -41,7 +41,9 @@ fn probe(pdev: &pci::Device<Core>, _info: &Self::IdInfo) -> Result<Pin<KBox<Self
>
>          let this = KBox::pin_init(
>              try_pin_init!(Self {
> -                gpu <- Gpu::new(pdev, bar)?,
> +                gpu <- Gpu::new(pdev, bar)?.pin_chain(|gpu| {
> +                    gpu.start_gsp(pdev)
> +                }),
>                  _reg: auxiliary::Registration::new(
>                      pdev.as_ref(),
>                      c_str!("nova-drm"),
> diff --git a/drivers/gpu/nova-core/gpu.rs b/drivers/gpu/nova-core/gpu.rs
> index 8caecaf7dfb4..211bc1a5a5b3 100644
> --- a/drivers/gpu/nova-core/gpu.rs
> +++ b/drivers/gpu/nova-core/gpu.rs
> @@ -266,7 +266,7 @@ fn run_fwsec_frts(
>      pub(crate) fn new(
>          pdev: &pci::Device<device::Bound>,
>          devres_bar: Arc<Devres<Bar0>>,
> -    ) -> Result<impl PinInit<Self>> {
> +    ) -> Result<impl PinInit<Self, Error>> {
>          let bar = devres_bar.access(pdev.as_ref())?;
>          let spec = Spec::new(bar)?;
>          let fw = Firmware::new(pdev.as_ref(), spec.chipset, FIRMWARE_VERSION)?;
> @@ -302,11 +302,16 @@ pub(crate) fn new(
>
>          Self::run_fwsec_frts(pdev.as_ref(), &gsp_falcon, bar, &bios, &fb_layout)?;
>
> -        Ok(pin_init!(Self {
> +        Ok(try_pin_init!(Self {
>              spec,
>              bar: devres_bar,
>              fw,
>              sysmem_flush,
>          }))
>      }
> +
> +    pub(crate) fn start_gsp(&self, _pdev: &pci::Device<device::Core>) -> Result {
> +        // noop
> +        Ok(())
> +    }
>  }
>
> But maybe it doesn't capture your intend?

The issue is that `start_gsp` returns a value (currently a placeholder
`()`, but it will change into a real type) that needs to be stored into
the newly-introduced `gsp` member of `NovaCore`. I could not figure how
how `pin_chain` could help with this (and this is the same problem for
the other `unsafe` statements in `firmware/gsp.rs`).

It is a common pattern when initializing a pinned object, so I agree it
would be nice support this without unsafe code.