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Message-Id: <DCJ46WGRUXR8.1GKGGL2568E1X@kernel.org>
Date: Wed, 03 Sep 2025 13:05:15 +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 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.
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