rust: io: mem: add a generic iomem abstraction

Add a generic iomem abstraction to safely read and write ioremapped
regions. This abstraction requires a previously acquired IoRequest
instance. This makes it so that both the resource and the device match,
or, in other words, that the resource is indeed a valid resource for a
given bound device.

A subsequent patch will add the ability to retrieve IoRequest instances
from platform devices.

The reads and writes are done through IoRaw, and are thus checked either
at compile-time, if the size of the region is known at that point, or at
runtime otherwise.

Non-exclusive access to the underlying memory region is made possible to
cater to cases where overlapped regions are unavoidable.

Acked-by: Miguel Ojeda <ojeda@kernel.org>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Daniel Almeida <daniel.almeida@collabora.com>
Link: https://lore.kernel.org/r/20250717-topics-tyr-platform_iomem-v15-2-beca780b77e3@collabora.com
[ Add #[expect(dead_code)] to avoid a temporary warning, remove
  unnecessary OF_ID_TABLE constants in doc-tests and ignore doc-tests
  for now to avoid a temporary build failure. - Danilo ]
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

rust/helpers/io.c

@@ -8,6 +8,11 @@ void __iomem *rust_helper_ioremap(phys_addr_t offset, size_t size)
 	return ioremap(offset, size);
 }
 
+void __iomem *rust_helper_ioremap_np(phys_addr_t offset, size_t size)
+{
+	return ioremap_np(offset, size);
+}
+
 void rust_helper_iounmap(void __iomem *addr)
 {
 	iounmap(addr);

rust/kernel/io.rs

@@ -7,6 +7,7 @@
 use crate::error::{code::EINVAL, Result};
 use crate::{bindings, build_assert};
 
+pub mod mem;
 pub mod resource;
 
 pub use resource::Resource;

rust/kernel/io/mem.rs

@@ -0,0 +1,280 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Generic memory-mapped IO.
+
+use core::ops::Deref;
+
+use crate::c_str;
+use crate::device::Bound;
+use crate::device::Device;
+use crate::devres::Devres;
+use crate::io;
+use crate::io::resource::Region;
+use crate::io::resource::Resource;
+use crate::io::Io;
+use crate::io::IoRaw;
+use crate::prelude::*;
+
+/// An IO request for a specific device and resource.
+pub struct IoRequest<'a> {
+    device: &'a Device<Bound>,
+    resource: &'a Resource,
+}
+
+impl<'a> IoRequest<'a> {
+    /// Creates a new [`IoRequest`] instance.
+    ///
+    /// # Safety
+    ///
+    /// Callers must ensure that `resource` is valid for `device` during the
+    /// lifetime `'a`.
+    #[expect(dead_code)]
+    pub(crate) unsafe fn new(device: &'a Device<Bound>, resource: &'a Resource) -> Self {
+        IoRequest { device, resource }
+    }
+
+    /// Maps an [`IoRequest`] where the size is known at compile time.
+    ///
+    /// This uses the [`ioremap()`] C API.
+    ///
+    /// [`ioremap()`]: https://docs.kernel.org/driver-api/device-io.html#getting-access-to-the-device
+    ///
+    /// # Examples
+    ///
+    /// The following example uses a [`platform::Device`] for illustration
+    /// purposes.
+    ///
+    /// ```ignore
+    /// use kernel::{bindings, c_str, platform, of, device::Core};
+    /// struct SampleDriver;
+    ///
+    /// impl platform::Driver for SampleDriver {
+    ///    # type IdInfo = ();
+    ///
+    ///    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_sized`].
+    ///       //
+    ///       // No runtime checks will apply when reading and writing.
+    ///       let request = pdev.io_request_by_index(0).ok_or(ENODEV)?;
+    ///       let iomem = request.iomap_sized::<42>();
+    ///       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_sized<const SIZE: usize>(self) -> impl PinInit<Devres<IoMem<SIZE>>, Error> + 'a {
+        IoMem::new(self)
+    }
+
+    /// Same as [`Self::iomap_sized`] but with exclusive access to the
+    /// underlying region.
+    ///
+    /// This uses the [`ioremap()`] C API.
+    ///
+    /// [`ioremap()`]: https://docs.kernel.org/driver-api/device-io.html#getting-access-to-the-device
+    pub fn iomap_exclusive_sized<const SIZE: usize>(
+        self,
+    ) -> impl PinInit<Devres<ExclusiveIoMem<SIZE>>, Error> + 'a {
+        ExclusiveIoMem::new(self)
+    }
+
+    /// Maps an [`IoRequest`] where the size is not known at compile time,
+    ///
+    /// This uses the [`ioremap()`] C API.
+    ///
+    /// [`ioremap()`]: https://docs.kernel.org/driver-api/device-io.html#getting-access-to-the-device
+    ///
+    /// # Examples
+    ///
+    /// The following example uses a [`platform::Device`] for illustration
+    /// purposes.
+    ///
+    /// ```ignore
+    /// use kernel::{bindings, c_str, platform, of, device::Core};
+    /// struct SampleDriver;
+    ///
+    /// impl platform::Driver for SampleDriver {
+    ///    # type IdInfo = ();
+    ///
+    ///    fn probe(
+    ///       pdev: &platform::Device<Core>,
+    ///       info: Option<&Self::IdInfo>,
+    ///    ) -> Result<Pin<KBox<Self>>> {
+    ///       let offset = 0; // Some offset.
+    ///
+    ///       // Unlike [`Self::iomap_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 request = pdev.io_request_by_index(0).ok_or(ENODEV)?;
+    ///       let iomem = request.iomap();
+    ///       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(self) -> impl PinInit<Devres<IoMem<0>>, Error> + 'a {
+        Self::iomap_sized::<0>(self)
+    }
+
+    /// Same as [`Self::iomap`] but with exclusive access to the underlying
+    /// region.
+    pub fn iomap_exclusive(self) -> impl PinInit<Devres<ExclusiveIoMem<0>>, Error> + 'a {
+        Self::iomap_exclusive_sized::<0>(self)
+    }
+}
+
+/// An exclusive memory-mapped IO region.
+///
+/// # Invariants
+///
+/// - [`ExclusiveIoMem`] has exclusive access to the underlying [`IoMem`].
+pub struct ExclusiveIoMem<const SIZE: usize> {
+    /// The underlying `IoMem` instance.
+    iomem: IoMem<SIZE>,
+
+    /// The region abstraction. This represents exclusive access to the
+    /// range represented by the underlying `iomem`.
+    ///
+    /// This field is needed for ownership of the region.
+    _region: Region,
+}
+
+impl<const SIZE: usize> ExclusiveIoMem<SIZE> {
+    /// Creates a new `ExclusiveIoMem` instance.
+    fn ioremap(resource: &Resource) -> Result<Self> {
+        let start = resource.start();
+        let size = resource.size();
+        let name = resource.name().unwrap_or(c_str!(""));
+
+        let region = resource
+            .request_region(
+                start,
+                size,
+                name.to_cstring()?,
+                io::resource::Flags::IORESOURCE_MEM,
+            )
+            .ok_or(EBUSY)?;
+
+        let iomem = IoMem::ioremap(resource)?;
+
+        let iomem = ExclusiveIoMem {
+            iomem,
+            _region: region,
+        };
+
+        Ok(iomem)
+    }
+
+    /// Creates a new `ExclusiveIoMem` instance from a previously acquired [`IoRequest`].
+    pub fn new<'a>(io_request: IoRequest<'a>) -> impl PinInit<Devres<Self>, Error> + 'a {
+        let dev = io_request.device;
+        let res = io_request.resource;
+
+        Devres::new(dev, Self::ioremap(res))
+    }
+}
+
+impl<const SIZE: usize> Deref for ExclusiveIoMem<SIZE> {
+    type Target = Io<SIZE>;
+
+    fn deref(&self) -> &Self::Target {
+        &self.iomem
+    }
+}
+
+/// A generic memory-mapped IO region.
+///
+/// Accesses to the underlying region is checked either at compile time, if the
+/// region's size is known at that point, or at runtime otherwise.
+///
+/// # Invariants
+///
+/// [`IoMem`] always holds an [`IoRaw`] instance that holds a valid pointer to the
+/// start of the I/O memory mapped region.
+pub struct IoMem<const SIZE: usize = 0> {
+    io: IoRaw<SIZE>,
+}
+
+impl<const SIZE: usize> IoMem<SIZE> {
+    fn ioremap(resource: &Resource) -> Result<Self> {
+        // Note: Some ioremap() implementations use types that depend on the CPU
+        // word width rather than the bus address width.
+        //
+        // TODO: Properly address this in the C code to avoid this `try_into`.
+        let size = resource.size().try_into()?;
+        if size == 0 {
+            return Err(EINVAL);
+        }
+
+        let res_start = resource.start();
+
+        let addr = if resource
+            .flags()
+            .contains(io::resource::Flags::IORESOURCE_MEM_NONPOSTED)
+        {
+            // SAFETY:
+            // - `res_start` and `size` are read from a presumably valid `struct resource`.
+            // - `size` is known not to be zero at this point.
+            unsafe { bindings::ioremap_np(res_start, size) }
+        } else {
+            // SAFETY:
+            // - `res_start` and `size` are read from a presumably valid `struct resource`.
+            // - `size` is known not to be zero at this point.
+            unsafe { bindings::ioremap(res_start, size) }
+        };
+
+        if addr.is_null() {
+            return Err(ENOMEM);
+        }
+
+        let io = IoRaw::new(addr as usize, size)?;
+        let io = IoMem { io };
+
+        Ok(io)
+    }
+
+    /// Creates a new `IoMem` instance from a previously acquired [`IoRequest`].
+    pub fn new<'a>(io_request: IoRequest<'a>) -> impl PinInit<Devres<Self>, Error> + 'a {
+        let dev = io_request.device;
+        let res = io_request.resource;
+
+        Devres::new(dev, Self::ioremap(res))
+    }
+}
+
+impl<const SIZE: usize> Drop for IoMem<SIZE> {
+    fn drop(&mut self) {
+        // SAFETY: Safe as by the invariant of `Io`.
+        unsafe { bindings::iounmap(self.io.addr() as *mut c_void) }
+    }
+}
+
+impl<const SIZE: usize> Deref for IoMem<SIZE> {
+    type Target = Io<SIZE>;
+
+    fn deref(&self) -> &Self::Target {
+        // SAFETY: Safe as by the invariant of `IoMem`.
+        unsafe { Io::from_raw(&self.io) }
+    }
+}