Re: [PATCH v4 12/13] rust: platform: add basic platform device / driver abstractions

[Danilo Krummrich]

On Mon, Dec 09, 2024 at 04:37:06PM -0600, Rob Herring wrote:
> On Thu, Dec 05, 2024 at 03:14:43PM +0100, Danilo Krummrich wrote:
> > Implement the basic platform bus abstractions required to write a basic
> > platform driver. This includes the following data structures:
> > 
> > The `platform::Driver` trait represents the interface to the driver and
> > provides `pci::Driver::probe` for the driver to implement.
> > 
> > The `platform::Device` abstraction represents a `struct platform_device`.
> > 
> > In order to provide the platform bus specific parts to a generic
> > `driver::Registration` the `driver::RegistrationOps` trait is implemented
> > by `platform::Adapter`.
> > 
> > Signed-off-by: Danilo Krummrich <dakr@xxxxxxxxxx>
> > ---
> >  MAINTAINERS                     |   1 +
> >  rust/bindings/bindings_helper.h |   2 +
> >  rust/helpers/helpers.c          |   1 +
> >  rust/helpers/platform.c         |  13 ++
> >  rust/kernel/lib.rs              |   1 +
> >  rust/kernel/platform.rs         | 222 ++++++++++++++++++++++++++++++++
> >  6 files changed, 240 insertions(+)
> >  create mode 100644 rust/helpers/platform.c
> >  create mode 100644 rust/kernel/platform.rs
> > 
> > diff --git a/MAINTAINERS b/MAINTAINERS
> > index 7d6bb4b15d2c..365fc48b7041 100644
> > --- a/MAINTAINERS
> > +++ b/MAINTAINERS
> > @@ -7034,6 +7034,7 @@ F:	rust/kernel/device.rs
> >  F:	rust/kernel/device_id.rs
> >  F:	rust/kernel/devres.rs
> >  F:	rust/kernel/driver.rs
> > +F:	rust/kernel/platform.rs
> >  
> >  DRIVERS FOR OMAP ADAPTIVE VOLTAGE SCALING (AVS)
> >  M:	Nishanth Menon <nm@xxxxxx>
> > diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
> > index 6d7a68e2ecb7..e9fdceb568b8 100644
> > --- a/rust/bindings/bindings_helper.h
> > +++ b/rust/bindings/bindings_helper.h
> > @@ -20,9 +20,11 @@
> >  #include <linux/jump_label.h>
> >  #include <linux/mdio.h>
> >  #include <linux/miscdevice.h>
> > +#include <linux/of_device.h>
> >  #include <linux/pci.h>
> >  #include <linux/phy.h>
> >  #include <linux/pid_namespace.h>
> > +#include <linux/platform_device.h>
> >  #include <linux/poll.h>
> >  #include <linux/refcount.h>
> >  #include <linux/sched.h>
> > diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c
> > index 3fda33cd42d4..0640b7e115be 100644
> > --- a/rust/helpers/helpers.c
> > +++ b/rust/helpers/helpers.c
> > @@ -20,6 +20,7 @@
> >  #include "kunit.c"
> >  #include "mutex.c"
> >  #include "page.c"
> > +#include "platform.c"
> >  #include "pci.c"
> >  #include "pid_namespace.c"
> >  #include "rbtree.c"
> > diff --git a/rust/helpers/platform.c b/rust/helpers/platform.c
> > new file mode 100644
> > index 000000000000..ab9b9f317301
> > --- /dev/null
> > +++ b/rust/helpers/platform.c
> > @@ -0,0 +1,13 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +
> > +#include <linux/platform_device.h>
> > +
> > +void *rust_helper_platform_get_drvdata(const struct platform_device *pdev)
> > +{
> > +	return platform_get_drvdata(pdev);
> > +}
> > +
> > +void rust_helper_platform_set_drvdata(struct platform_device *pdev, void *data)
> > +{
> > +	platform_set_drvdata(pdev, data);
> > +}
> > diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
> > index 7a0e4c82ad0c..cc8f48aa162b 100644
> > --- a/rust/kernel/lib.rs
> > +++ b/rust/kernel/lib.rs
> > @@ -59,6 +59,7 @@
> >  pub mod of;
> >  pub mod page;
> >  pub mod pid_namespace;
> > +pub mod platform;
> >  pub mod prelude;
> >  pub mod print;
> >  pub mod rbtree;
> > diff --git a/rust/kernel/platform.rs b/rust/kernel/platform.rs
> > new file mode 100644
> > index 000000000000..868cfddb75a2
> > --- /dev/null
> > +++ b/rust/kernel/platform.rs
> > @@ -0,0 +1,222 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +
> > +//! Abstractions for the platform bus.
> > +//!
> > +//! C header: [`include/linux/platform_device.h`](srctree/include/linux/platform_device.h)
> > +
> > +use crate::{
> > +    bindings, container_of, device, driver,
> > +    error::{to_result, Result},
> > +    of,
> > +    prelude::*,
> > +    str::CStr,
> > +    types::{ARef, ForeignOwnable},
> > +    ThisModule,
> > +};
> > +
> > +/// An adapter for the registration of platform drivers.
> > +pub struct Adapter<T: Driver>(T);
> > +
> > +impl<T: Driver + 'static> driver::RegistrationOps for Adapter<T> {
> > +    type RegType = bindings::platform_driver;
> > +
> > +    fn register(
> > +        pdrv: &mut Self::RegType,
> > +        name: &'static CStr,
> > +        module: &'static ThisModule,
> > +    ) -> Result {
> > +        pdrv.driver.name = name.as_char_ptr();
> > +        pdrv.probe = Some(Self::probe_callback);
> > +
> > +        // Both members of this union are identical in data layout and semantics.
> > +        pdrv.__bindgen_anon_1.remove = Some(Self::remove_callback);
> > +        pdrv.driver.of_match_table = T::OF_ID_TABLE.as_ptr();
> > +
> > +        // SAFETY: `pdrv` is guaranteed to be a valid `RegType`.
> > +        to_result(unsafe { bindings::__platform_driver_register(pdrv, module.0) })
> > +    }
> > +
> > +    fn unregister(pdrv: &mut Self::RegType) {
> > +        // SAFETY: `pdrv` is guaranteed to be a valid `RegType`.
> > +        unsafe { bindings::platform_driver_unregister(pdrv) };
> > +    }
> > +}
> > +
> > +impl<T: Driver + 'static> Adapter<T> {
> > +    #[cfg(CONFIG_OF)]
> > +    fn of_id_info(pdev: &Device) -> Option<&'static T::IdInfo> {
> > +        let table = T::OF_ID_TABLE;
> > +
> > +        // SAFETY:
> > +        // - `table` has static lifetime, hence it's valid for read,
> > +        // - `dev` is guaranteed to be valid while it's alive, and so is `pdev.as_ref().as_raw()`.
> > +        let raw_id = unsafe { bindings::of_match_device(table.as_ptr(), pdev.as_ref().as_raw()) };
> > +
> > +        if raw_id.is_null() {
> > +            None
> > +        } else {
> > +            // SAFETY: `DeviceId` is a `#[repr(transparent)` wrapper of `struct of_device_id` and
> > +            // does not add additional invariants, so it's safe to transmute.
> > +            let id = unsafe { &*raw_id.cast::<of::DeviceId>() };
> > +
> > +            Some(table.info(<of::DeviceId as crate::device_id::RawDeviceId>::index(id)))
> > +        }
> > +    }
> > +
> > +    #[cfg(not(CONFIG_OF))]
> > +    fn of_id_info(_pdev: &Device) -> Option<&'static T::IdInfo> {
> > +        None
> > +    }
> > +
> > +    // Try to retrieve an `IdInfo` from any of the ID tables; if we can't find one for a particular
> > +    // table, it means we don't have a match in there. If we don't match any of the ID tables, it
> > +    // means we were matched by name.
> > +    fn id_info(pdev: &Device) -> Option<&'static T::IdInfo> {
> > +        let id = Self::of_id_info(pdev);
> > +        if id.is_some() {
> > +            return id;
> > +        }
> > +
> > +        None
> > +    }
> 
> These methods are going to have to be duplicated by every bus type which 
> can do DT matching (and later ACPI). Can't this be moved to be part of 
> the common Driver trait.

As mentioned in v3, I agree, but I'd prefer to do this in a follow up series.

> 
> 
> I'll say it again for Greg to comment (doubtful he will look at v3 
> again). Really, I think we should also align the probe method interface 
> across bus types. That means getting rid of the 'id' in the PCI probe 
> (or add it for everyone). Most drivers never need it. The typical case 
> is needing nothing or the matched data. In a quick scan[1], there's 
> only a handful of cases. So I think probe should match the common 
> scenario and make retrieving the id match explicit if needed.

I agree, but I will keep it until Greg commented on it, since I explicitly
promised to add it on request.

> 
> Rob
> 
> [1] git grep -W 'const struct pci_device_id \*' drivers/ | grep -P 'id->(?!driver_data)'