Re: [PATCH v9 4/4] rust: platform: allow ioremap of platform resources

[Danilo Krummrich <dakr@kernel.org>]

On Tue, Jun 03, 2025 at 12:05:30PM -0300, Daniel Almeida wrote:
> The preceding patches added support for resources, and for a general
> IoMem abstraction, but thus far there is no way to access said IoMem
> from drivers, as its creation is unsafe and depends on a resource that
> must be acquired from some device first.
> 
> Now, allow the ioremap of platform resources themselves, thereby making
> the IoMem available to platform drivers.
> 
> Signed-off-by: Daniel Almeida <daniel.almeida@collabora.com>
> ---
>  rust/kernel/platform.rs | 123 +++++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 121 insertions(+), 2 deletions(-)
> 
> diff --git a/rust/kernel/platform.rs b/rust/kernel/platform.rs
> index 427bc706f4349083b6bab81a02cb8ed803903590..57414fd0db296e412f45fbefd7707b338b37332a 100644
> --- a/rust/kernel/platform.rs
> +++ b/rust/kernel/platform.rs
> @@ -5,9 +5,14 @@
>  //! C header: [`include/linux/platform_device.h`](srctree/include/linux/platform_device.h)
>  
>  use crate::{
> -    bindings, container_of, device, driver,
> +    bindings, container_of, device,
> +    devres::Devres,
> +    driver,
>      error::{to_result, Result},
> -    io::resource::Resource,
> +    io::{
> +        mem::{ExclusiveIoMem, IoMem},
> +        resource::Resource,

I think we should add

	pub use resource::Resource;

into io.rs, such that we can refer to this as ::kernel::io::Resource.

> +    },
>      of,
>      prelude::*,
>      str::CStr,
> @@ -227,6 +232,120 @@ pub fn resource_by_name(&self, name: &CStr) -> Option<&Resource> {
>      }
>  }
>  
> +impl Device<device::Bound> {
> +    /// Maps a platform resource where the size is known at compile time.
> +    ///
> +    /// This uses the
> +    /// [`ioremap()`](https://docs.kernel.org/driver-api/device-io.html#getting-access-to-the-device)
> +    /// C API.
> +    ///
> +    /// # Examples
> +    ///
> +    /// ```no_run
> +    /// # use kernel::{bindings, c_str, platform, of, device::Core};
> +    /// # struct SampleDriver;
> +    ///
> +    /// impl platform::Driver for SampleDriver {
> +    ///    # type IdInfo = ();
> +    ///    # const OF_ID_TABLE: Option<of::IdTable<Self::IdInfo>> = None;
> +    ///
> +    ///    fn probe(
> +    ///       pdev: &platform::Device<Core>,
> +    ///       info: Option<&Self::IdInfo>,
> +    ///    ) -> Result<Pin<KBox<Self>>> {
> +    ///       let offset = 0; // Some offset.
> +    ///
> +    ///       // If the size is known at compile time, use [`Self::iomap_resource_sized`].
> +    ///       //
> +    ///       // No runtime checks will apply when reading and writing.
> +    ///       let resource = pdev.resource_by_index(0).ok_or(ENODEV)?;
> +    ///       let iomem = pdev.iomap_resource_sized::<42>(&resource)?;
> +    ///       let io = iomem.access(pdev.as_ref())?;
> +    ///
> +    ///       // Read and write a 32-bit value at `offset`. Calling `try_access()` on
> +    ///       // the `Devres` makes sure that the resource is still valid.
> +    ///       let data = io.read32_relaxed(offset);
> +    ///
> +    ///       iomem.try_access().ok_or(ENODEV)?.write32_relaxed(data, offset);

io.write32_relaxed(data, offset);

> +    ///
> +    ///       # let sample_driver = KBox::new(SampleDriver, GFP_KERNEL).map_err(|_| ENOMEM)?;

Why the map_err()? We have

	impl From<AllocError> for Error {
	    fn from(_: AllocError) -> Error {
	        code::ENOMEM
	    }
	}

so you shouldn't need that.

Also, please just write this as

	# Ok(KBox::new(SampleDriver, GFP_KERNEL)?.into())

> +    ///       # Ok(sample_driver.into())
> +    ///     }
> +    /// }
> +    /// ```
> +    pub fn iomap_resource_sized<const SIZE: usize>(
> +        &self,
> +        resource: &Resource,
> +    ) -> Result<Devres<IoMem<SIZE>>> {
> +        IoMem::new(resource, self.as_ref())
> +    }
> +
> +    /// Same as [`Self::iomap_resource_sized`] but with exclusive access to the
> +    /// underlying region.
> +    ///
> +    /// This uses the
> +    /// [`ioremap()`](https://docs.kernel.org/driver-api/device-io.html#getting-access-to-the-device)
> +    /// C API.
> +    pub fn iomap_resource_exclusive_sized<const SIZE: usize>(
> +        &self,
> +        resource: &Resource,
> +    ) -> Result<Devres<ExclusiveIoMem<SIZE>>> {
> +        ExclusiveIoMem::new(resource, self.as_ref())
> +    }
> +
> +    /// Maps a platform resource through iomap().
> +    ///
> +    /// This uses the
> +    /// [`ioremap()`](https://docs.kernel.org/driver-api/device-io.html#getting-access-to-the-device)
> +    /// C API.
> +    ///
> +    /// # Examples
> +    ///
> +    /// ```no_run
> +    /// # use kernel::{bindings, c_str, platform, of, device::Core};
> +    /// # struct SampleDriver;
> +    ///
> +    /// impl platform::Driver for SampleDriver {
> +    ///    # type IdInfo = ();
> +    ///    # const OF_ID_TABLE: Option<of::IdTable<Self::IdInfo>> = None;
> +    ///
> +    ///    fn probe(
> +    ///       pdev: &platform::Device<Core>,
> +    ///       info: Option<&Self::IdInfo>,
> +    ///    ) -> Result<Pin<KBox<Self>>> {
> +    ///       let offset = 0; // Some offset.
> +    ///
> +    ///       // Unlike [`Self::iomap_resource_sized`], here the size of the memory region
> +    ///       // is not known at compile time, so only the `try_read*` and `try_write*`
> +    ///       // family of functions should be used, leading to runtime checks on every
> +    ///       // access.
> +    ///       let resource = pdev.resource_by_index(0).ok_or(ENODEV)?;
> +    ///       let iomem = pdev.iomap_resource(&resource)?;
> +    ///       let io = iomem.access(pdev.as_ref())?;
> +    ///
> +    ///       let data = io.try_read32_relaxed(offset)?;
> +    ///
> +    ///       io.try_write32_relaxed(data, offset)?;
> +    ///
> +    ///       # let sample_driver = KBox::new(SampleDriver, GFP_KERNEL).map_err(|_| ENOMEM)?;

Same as above.

> +    ///       # Ok(sample_driver.into())
> +    ///     }
> +    /// }
> +    /// ```
> +    pub fn iomap_resource(&self, resource: &Resource) -> Result<Devres<IoMem<0>>> {
> +        self.iomap_resource_sized::<0>(resource)
> +    }
> +
> +    /// Same as [`Self::iomap_resource`] but with exclusive access to the underlying
> +    /// region.
> +    pub fn iomap_resource_exclusive(
> +        &self,
> +        resource: &Resource,
> +    ) -> Result<Devres<ExclusiveIoMem<0>>> {
> +        self.iomap_resource_exclusive_sized::<0>(resource)
> +    }
> +}
> +
>  // SAFETY: `Device` is a transparent wrapper of a type that doesn't depend on `Device`'s generic
>  // argument.
>  kernel::impl_device_context_deref!(unsafe { Device });
> 
> -- 
> 2.49.0
>