Re: [PATCH 4/4] rust: platform: fix unrestricted &mut platform::Device

[Danilo Krummrich <dakr@kernel.org>]

On Thu, Mar 13, 2025 at 10:49:59AM +0000, Benno Lossin wrote:
> On Thu Mar 13, 2025 at 3:13 AM CET, Danilo Krummrich wrote:
> > As by now, platform::Device is implemented as:
> >
> > 	#[derive(Clone)]
> > 	pub struct Device(ARef<device::Device>);
> >
> > This may be convenient, but has the implication that drivers can call
> > device methods that require a mutable reference concurrently at any
> > point of time.
> 
> Similar to the other patch, I didn't find any methods taking `&mut self`
> but I might have missed them.

`platform::Device` does not have any yet. But we still need the pattern. Once we
land the `dma::Device` trait, we'll need:

	impl dma::Device for platform::Device<Core> {}

to derive the DMA methods.

Besides that, I want bus device implementations to be consistent.

> 
> > Instead define platform::Device as
> >
> > 	pub struct Device<Ctx: DeviceContext = Normal>(
> > 		Opaque<bindings::platform_dev>,
> > 		PhantomData<Ctx>,
> > 	);
> >
> > and manually implement the AlwaysRefCounted trait.
> >
> > With this we can implement methods that should only be called from
> > bus callbacks (such as probe()) for platform::Device<Core>. Consequently,
> > we make this type accessible in bus callbacks only.
> >
> > Arbitrary references taken by the driver are still of type
> > ARef<platform::Device> and hence don't provide access to methods that are
> > reserved for bus callbacks.
> >
> > Fixes: 683a63befc73 ("rust: platform: add basic platform device / driver abstractions")
> > Signed-off-by: Danilo Krummrich <dakr@kernel.org>
> 
> The same two nits from patch #3 also apply.
> 
> Reviewed-by: Benno Lossin <benno.lossin@proton.me>
> 
> ---
> Cheers,
> Benno
> 
> > ---
> >  rust/kernel/platform.rs              | 93 ++++++++++++++++++----------
> >  samples/rust/rust_driver_platform.rs | 16 +++--
> >  2 files changed, 74 insertions(+), 35 deletions(-)
>