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

[Danilo Krummrich <dakr@kernel.org>]

On Tue, Dec 10, 2024 at 08:46:29AM +0100, Greg KH wrote:
> 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@kernel.org>
> > > ---
> > >  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@ti.com>
> > > 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.
> > 
> > 
> > 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.
> 
> If there's a way for the probe callback to get access to the id that
> caused it to match, then it's fine with me to remove it.  But is that
> possible?  Many many drivers encode "stuff" in the id that the driver
> needs to know (quirks, functions, etc.)

The signature would be

`fn probe(dev: &mut Device, id_info: &Self::IdInfo) -> Result<Pin<KBox<Self>>>`

where `id_info` is the driver private data.

The other fields of struct pci_device_id should also be available from struct
pci_dev`, i.e. `dev`; just need to add the corresponding accessors for it.

- Danilo

> 
> If that's not possible, then it needs to stay.
> 
> thanks,
> 
> greg k-h