linux-kernel - Re: [PATCH v3 15/16] rust: platform: add basic platform device / driver abstractions

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Message-ID: <ZyCvyrb5jsY1O4uX@pollux>
Date: Tue, 29 Oct 2024 10:50:02 +0100
From: Danilo Krummrich <dakr@...nel.org>
To: Dirk Behme <dirk.behme@...bosch.com>
Cc: gregkh@...uxfoundation.org, rafael@...nel.org, bhelgaas@...gle.com,
	ojeda@...nel.org, alex.gaynor@...il.com, boqun.feng@...il.com,
	gary@...yguo.net, bjorn3_gh@...tonmail.com, benno.lossin@...ton.me,
	tmgross@...ch.edu, a.hindborg@...sung.com, aliceryhl@...gle.com,
	airlied@...il.com, fujita.tomonori@...il.com, lina@...hilina.net,
	pstanner@...hat.com, ajanulgu@...hat.com, lyude@...hat.com,
	robh@...nel.org, daniel.almeida@...labora.com, saravanak@...gle.com,
	rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH v3 15/16] rust: platform: add basic platform device /
 driver abstractions

On Tue, Oct 29, 2024 at 10:19:08AM +0100, Dirk Behme wrote:
> On 29.10.2024 09:50, Danilo Krummrich wrote:
> > On Tue, Oct 29, 2024 at 08:20:55AM +0100, Dirk Behme wrote:
> > > On 28.10.2024 11:19, Danilo Krummrich wrote:
> > > > On Thu, Oct 24, 2024 at 11:11:50AM +0200, Dirk Behme wrote:
> > > > > > +/// IdTable type for platform drivers.
> > > > > > +pub type IdTable<T> = &'static dyn kernel::device_id::IdTable<of::DeviceId, T>;
> > > > > > +
> > > > > > +/// The platform driver trait.
> > > > > > +///
> > > > > > +/// # Example
> > > > > > +///
> > > > > > +///```
> > > > > > +/// # use kernel::{bindings, c_str, of, platform};
> > > > > > +///
> > > > > > +/// struct MyDriver;
> > > > > > +///
> > > > > > +/// kernel::of_device_table!(
> > > > > > +///     OF_TABLE,
> > > > > > +///     MODULE_OF_TABLE,
> > > > > 
> > > > > It looks to me that OF_TABLE and MODULE_OF_TABLE are quite generic names
> > > > > used here. Shouldn't they be somehow driver specific, e.g. OF_TABLE_MYDRIVER
> > > > > and MODULE_OF_TABLE_MYDRIVER or whatever? Same for the other
> > > > > examples/samples in this patch series. Found that while using the *same*
> > > > > somewhere else ;)
> > > > 
> > > > I think the names by themselves are fine. They're local to the module. However,
> > > > we stringify `OF_TABLE` in `module_device_table` to build the export name, i.e.
> > > > "__mod_of__OF_TABLE_device_table". Hence the potential duplicate symbols.
> > > > 
> > > > I think we somehow need to build the module name into the symbol name as well.
> > > 
> > > Something like this?
> > 
> > No, I think we should just encode the Rust module name / path, which should make
> > this a unique symbol name.
> > 
> > diff --git a/rust/kernel/device_id.rs b/rust/kernel/device_id.rs
> > index 5b1329fba528..63e81ec2d6fd 100644
> > --- a/rust/kernel/device_id.rs
> > +++ b/rust/kernel/device_id.rs
> > @@ -154,7 +154,7 @@ macro_rules! module_device_table {
> >       ($table_type: literal, $module_table_name:ident, $table_name:ident) => {
> >           #[rustfmt::skip]
> >           #[export_name =
> > -            concat!("__mod_", $table_type, "__", stringify!($table_name), "_device_table")
> > +            concat!("__mod_", $table_type, "__", module_path!(), "_", stringify!($table_name), "_device_table")
> >           ]
> >           static $module_table_name: [core::mem::MaybeUninit<u8>; $table_name.raw_ids().size()] =
> >               unsafe { core::mem::transmute_copy($table_name.raw_ids()) };
> > 
> > For the doctests for instance this
> > 
> >    "__mod_of__OF_TABLE_device_table"
> > 
> > becomes
> > 
> >    "__mod_of__doctests_kernel_generated_OF_TABLE_device_table".
> 
> 
> What implies *one* OF/PCI_TABLE per path (file)?

No, you can still have as many as you want for the same file, you just have to
give them different identifier names -- you can't have two statics with the same
name in one file anyways.

Well, I guess you somehow can (just like the doctests do), but it does make
sense to declare drivers in such a way.

I think as long as we take care that separate Rust modules can't interfere with
each other it's good enough.

> 
> For example adding a second FooDriver example to platform.rs won't be
> possible?

Not unless you change the identifier name unfortunately. But that might be
fixable by putting doctests in separate `mod $(DOCTEST) {}` blocks.

> 
> +/// struct FooDriver;
> +///
> +/// kernel::of_device_table!(
> +///     OF_TABLE,
> +///     MODULE_OF_TABLE,
> +///     <FooDriver as platform::Driver>::IdInfo,
> +///     [
> +///         (of::DeviceId::new(c_str!("test,rust-device2")), ())
> +///     ]
> +/// );
> 
> Best regards
> 
> Dirk
> 
> 
> 
>