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 | 127 +++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 125 insertions(+), 2 deletions(-)

diff --git a/rust/kernel/platform.rs b/rust/kernel/platform.rs
index bafd3ccea6d15b7965d1a993deef3f58e03b3490..b2c17fd6ab990c0b5ae6d6ed2e466b199eae2536 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::{
-    acpi, bindings, container_of, device, driver,
+    acpi, bindings, container_of, device,
+    devres::Devres,
+    driver,
     error::{to_result, Result},
-    io::Resource,
+    io::{
+        mem::{ExclusiveIoMem, IoMem},
+        Resource,
+    },
     of,
     prelude::*,
     str::CStr,
@@ -251,6 +256,124 @@ 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 iomem = KBox::pin_init(iomem, GFP_KERNEL)?;
+    ///
+    ///       let io = iomem.access(pdev.as_ref())?;
+    ///
+    ///       // Read and write a 32-bit value at `offset`.
+    ///       let data = io.read32_relaxed(offset);
+    ///
+    ///       io.write32_relaxed(data, offset);
+    ///
+    ///       # Ok(KBox::new(SampleDriver, GFP_KERNEL)?.into())
+    ///     }
+    /// }
+    /// ```
+    pub fn iomap_resource_sized<const SIZE: usize>(
+        &self,
+        resource: &Resource,
+    ) -> Result<impl PinInit<Devres<IoMem<SIZE>>, Error> + '_> {
+        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<impl PinInit<Devres<ExclusiveIoMem<SIZE>>, Error> + '_> {
+        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 iomem = KBox::pin_init(iomem, GFP_KERNEL)?;
+    ///
+    ///       let io = iomem.access(pdev.as_ref())?;
+    ///
+    ///       let data = io.try_read32_relaxed(offset)?;
+    ///
+    ///       io.try_write32_relaxed(data, offset)?;
+    ///
+    ///       # Ok(KBox::new(SampleDriver, GFP_KERNEL)?.into())
+    ///     }
+    /// }
+    /// ```
+    pub fn iomap_resource(
+        &self,
+        resource: &Resource,
+    ) -> Result<impl PinInit<Devres<IoMem<0>>, Error> + '_> {
+        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<impl PinInit<Devres<ExclusiveIoMem<0>>, Error> + '_> {
+        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 });

-- 
2.50.0

On 7/1/25 4:34 PM, Daniel Almeida wrote:
> +impl Device<device::Bound> {

<snip>

> +    pub fn iomap_resource_sized<const SIZE: usize>(
> +        &self,
> +        resource: &Resource,
> +    ) -> Result<impl PinInit<Devres<IoMem<SIZE>>, Error> + '_> {
> +        IoMem::new(resource, self.as_ref())
> +    }

Sorry that I did not catch this earlier, but what if I supply a Resource here
that has *not* been obtained by any of the platform::Device methods and from the
same platform::Device as you call this function for?

I think this also needs something similar to what we do in the IRQ abstraction,
e.g.:

	/// # Invariants
	///
	/// `res` has been obtained from `dev`.
	pub struct IoRequest<'a> {
	   dev: &'a Device<Bound>,
	   res: &'a Resource,
	}

Such that IoMem::new() can take an IoRequest instance instead.