On Fri, Jun 27, 2025 at 01:33:41AM +0200, Benno Lossin wrote:
> On Thu Jun 26, 2025 at 10:00 PM CEST, Danilo Krummrich wrote:
> > diff --git a/drivers/gpu/nova-core/gpu.rs b/drivers/gpu/nova-core/gpu.rs
> > index 60b86f370284..47653c14838b 100644
> > --- a/drivers/gpu/nova-core/gpu.rs
> > +++ b/drivers/gpu/nova-core/gpu.rs
>
> > @@ -161,14 +161,14 @@ fn new(bar: &Bar0) -> Result<Spec> {
> > pub(crate) struct Gpu {
> > spec: Spec,
> > /// MMIO mapping of PCI BAR 0
> > - bar: Devres<Bar0>,
> > + bar: Arc<Devres<Bar0>>,
>
> Can't you store it inline, given that you return an `impl PinInit<Self>`
> below?
I could, but I already know that we'll have to share bar later on.
> > fw: Firmware,
> > }
> >
> > impl Gpu {
> > pub(crate) fn new(
> > pdev: &pci::Device<device::Bound>,
> > - devres_bar: Devres<Bar0>,
> > + devres_bar: Arc<Devres<Bar0>>,
> > ) -> Result<impl PinInit<Self>> {
>
> While I see this code, is it really necessary to return `Result`
> wrapping the initializer here? I think it's probably better to return
> `impl PinInit<Self, Error>` instead. (of course in a different patch/an
> issue)
I will double check, but it's rather unlikely it makes sense. There's a lot of
initialization going on in Gpu::new(), the try_pin_init! call would probably get
too crazy.
>
> > let bar = devres_bar.access(pdev.as_ref())?;
> > let spec = Spec::new(bar)?;
>
> > @@ -44,6 +49,10 @@ struct DevresInner<T: Send> {
> > /// [`Devres`] users should make sure to simply free the corresponding backing resource in `T`'s
> > /// [`Drop`] implementation.
> > ///
> > +/// # Invariants
> > +///
> > +/// [`Self::inner`] is guaranteed to be initialized and is always accessed read-only.
> > +///
>
> Let's put this section below the examples, I really ought to write the
> safety docs one day and let everyone vote on this kind of stuff...
Sure!
> > /// # Example
> > ///
> > /// ```no_run
>
> > @@ -213,44 +233,63 @@ pub fn new(dev: &Device<Bound>, data: T, flags: Flags) -> Result<Self> {
> > /// }
> > /// ```
> > pub fn access<'a>(&'a self, dev: &'a Device<Bound>) -> Result<&'a T> {
> > - if self.0.dev.as_raw() != dev.as_raw() {
> > + if self.dev.as_raw() != dev.as_raw() {
> > return Err(EINVAL);
> > }
> >
> > // SAFETY: `dev` being the same device as the device this `Devres` has been created for
> > - // proves that `self.0.data` hasn't been revoked and is guaranteed to not be revoked as
> > - // long as `dev` lives; `dev` lives at least as long as `self`.
> > - Ok(unsafe { self.0.data.access() })
> > + // proves that `self.data` hasn't been revoked and is guaranteed to not be revoked as long
> > + // as `dev` lives; `dev` lives at least as long as `self`.
>
> What if the device has been unbound and a new device has been allocated
> in the exact same memory?
Unbound doesn't mean freed. Devres holds a reference of the device is was
created with, so it is impossible that it has been freed.
