Re: [PATCH v4 2/3] rust: io: mem: add a generic iomem abstraction

[Alice Ryhl]

On Thu, Jan 9, 2025 at 4:34 PM Daniel Almeida
<daniel.almeida@xxxxxxxxxxxxx> wrote:
>
> Hi Alice,
>
> >
> >> +pub struct IoMem<const SIZE: usize = 0> {
> >> +    io: IoRaw<SIZE>,
> >> +    res_start: u64,
> >> +    exclusive: bool,
> >
> > I don't think you need this after the `new` call, so you can remove
> > the field from the struct.
>
> Remove what?
>
> Both res_start and exclusive are used in IoMem::drop().

Ah ... I don't think exclusive should be a runtime value. I'd probably
have two types or move it to a const generic.

Or if we only need exclusive for now, then just drop exclusive.

> >> +    /// # Safety
> >> +    ///
> >> +    /// The caller must ensure that the underlying resource remains valid
> >> +    /// throughout the `IoMem`'s lifetime. This is usually done by wrapping the
> >> +    /// `IoMem` in a `Devres` instance, which will properly revoke the access
> >> +    /// when the device is unbound from the matched driver.
> >
> > I know that this is a requirement for IoRaw, but does the
> > `request_mem_region` call not guarantee that the memory region stays
> > valid until `drop` runs?
>
> Hmm, I don’t think so. I’d expect the lifetime of the iomem to be tied to the lifetime
> of the device, really. The mapping will probably remain, but other infrastructure will probably
> be shutdown, like the clocks or regulators, so accessing the region will probably deadlock in such cases.
>
> Other people feel free to correct me, of course ^

Ah, okay.

Alice