Re: [PATCH v6 2/3] rust: io: mem: add a generic iomem abstraction

[Daniel Sedlak <daniel@sedlak.dev>]

Hi,

On 1/30/25 11:05 PM, Daniel Almeida wrote:
> Add a generic iomem abstraction to safely read and write ioremapped
> regions.
> 
> 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.
> 
> Signed-off-by: Daniel Almeida <daniel.almeida@collabora.com>
> ---
>   rust/kernel/io.rs     |   1 +
>   rust/kernel/io/mem.rs | 125 ++++++++++++++++++++++++++++++++++++++++++
>   2 files changed, 126 insertions(+)
>   create mode 100644 rust/kernel/io/mem.rs
> 
> diff --git a/rust/kernel/io.rs b/rust/kernel/io.rs
> index 566d8b177e01..9ce3482b5ecd 100644
> --- a/rust/kernel/io.rs
> +++ b/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;
>   
>   /// Raw representation of an MMIO region.
> diff --git a/rust/kernel/io/mem.rs b/rust/kernel/io/mem.rs
> new file mode 100644
> index 000000000000..f87433ed858e
> --- /dev/null
> +++ b/rust/kernel/io/mem.rs
> @@ -0,0 +1,125 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +//! Generic memory-mapped IO.
> +
> +use core::ops::Deref;
> +
> +use crate::device::Device;
> +use crate::devres::Devres;
> +use crate::io::resource::Region;
> +use crate::io::resource::Resource;
> +use crate::io::Io;
> +use crate::io::IoRaw;
> +use crate::prelude::*;
> +
> +/// An exclusive memory-mapped IO region.
> +///
> +/// # Invariants
> +///
> +/// - ExclusiveIoMem has exclusive access to the underlying `iomem`.

formatting: ExclusiveIoMem -> [`ExclusiveIoMem`]?

> +pub struct ExclusiveIoMem<const SIZE: usize> {
> +    /// The region abstraction. This represents exclusive access to the
> +    /// range represented by the underlying `iomem`.
> +    ///
> +    /// It's placed first to ensure that the region is released before it is
> +    /// unmapped as a result of the drop order.
> +    #[allow(dead_code)]
> +    region: Region,
> +    /// The underlying `IoMem` instance.
> +    iomem: IoMem<SIZE>,
> +}
> +
> +impl<const SIZE: usize> ExclusiveIoMem<SIZE> {
> +    /// Creates a new `ExclusiveIoMem` instance.
> +    pub(crate) fn ioremap(resource: &Resource) -> Result<Self> {
> +        let iomem = IoMem::ioremap(resource)?;
> +
> +        let start = resource.start();
> +        let size = resource.size();
> +        let name = resource.name();
> +
> +        let region = resource
> +            .request_mem_region(start, size, name)
> +            .ok_or(EBUSY)?;
> +
> +        let iomem = ExclusiveIoMem { iomem, region };
> +
> +        Ok(iomem)
> +    }
> +
> +    pub(crate) fn new(resource: &Resource, device: &Device) -> Result<Devres<Self>> {
> +        let iomem = Self::ioremap(resource)?;
> +        let devres = Devres::new(device, iomem, GFP_KERNEL)?;
> +
> +        Ok(devres)
> +    }
> +}
> +
> +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` inststance that holds a valid pointer to the

typo: inststance -> instance
> +/// 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> {
> +        let size = resource.size();
> +        if size == 0 {
> +            return Err(EINVAL);
> +        }
> +
> +        let res_start = resource.start();
> +
> +        // SAFETY:
> +        // - `res_start` and `size` are read from a presumably valid `struct resource`.
> +        // - `size` is known not to be zero at this point.
> +        let addr = unsafe { bindings::ioremap(res_start, size as kernel::ffi::c_ulong) };
> +        if addr.is_null() {
> +            return Err(ENOMEM);
> +        }
> +
> +        let io = IoRaw::new(addr as usize, size as usize)?;
> +        let io = IoMem { io };
> +
> +        Ok(io)
> +    }
> +
> +    /// Creates a new `IoMem` instance.
> +    pub(crate) fn new(resource: &Resource, device: &Device) -> Result<Devres<Self>> {
> +        let io = Self::ioremap(resource)?;
> +        let devres = Devres::new(device, io, GFP_KERNEL)?;
> +
> +        Ok(devres)
> +    }
> +}
> +
> +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 core::ffi::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) }
> +    }
> +}
	Daniel