Message-Id: <DCJ0T81CZQ88.6IK6LG0E0R02@kernel.org>
Date: Wed, 03 Sep 2025 10:26:20 +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 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?

>>
>> 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?
>
> I've counted 16 uses of `unsafe`. :)

I did a grep | wc on the mbox file, so it includes the 5 additional occurrences
from the annotations. :)

Otherwise the 9 "real" ones I counted seem to match the 3 bindgen ones (fine of
course) plus the 5 ones from the pin initializers (we should avoid them).

>
> - 3 in the bindgen-generated code (these can't be avoided),
> - 7 to implement `FromBytes`,
> - 1 to work around the fact that `FromBytes` doesn't work on slices yet
>   (maybe that one can be removed)
> - 5 as a result of intra-dependencies in PinInit initializers (which we
>   might be able to remove if I figure out how to use `pin_chain`).
>
> So best-case scenario would be that we will be down to 10 that are truly
> unavoidable.

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