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

["Danilo Krummrich" <dakr@kernel.org>]

On Wed Sep 3, 2025 at 12:44 PM CEST, Alexandre Courbot wrote:
> 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`).

Ok, I see, I think Benno is already working on a solution to access previously
initialized fields from subsequent initializers.

@Benno: What's the status of this? I haven't seen an issue for that in the
pin-init GitHub repo, should we create one?

However, in this case I'm a bit confused why we want Gsp next to Gpu? Why not
just make Gsp a member of Gpu then?

I thought the intent was to keep temporary values local to start_gsp() and not
store them next to Gpu in the same allocation?

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