Re: [PATCH RESEND v5 2/3] rust: io: mem: add a generic iomem abstraction

Christian Schrefl
2025-01-16T21:15:24Z

Hi Daniel

On 16.01.25 1:56 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/helpers/io.c | 10 +++++
> rust/kernel/io.rs | 1 +
> rust/kernel/io/mem.rs | 98 +++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 109 insertions(+)
> create mode 100644 rust/kernel/io/mem.rs
>
> diff --git a/rust/helpers/io.c b/rust/helpers/io.c
> index 3cb47bd01942..cb10060c08ae 100644
> --- a/rust/helpers/io.c
> +++ b/rust/helpers/io.c
> @@ -106,3 +106,13 @@ resource_size_t rust_helper_resource_size(struct resource *res)
> return resource_size(res);
> }
>
> +struct resource *rust_helper_request_mem_region(resource_size_t start, resource_size_t n,
> + const char *name)
> +{
> + return request_mem_region(start, n, name);
> +}
> +
> +void rust_helper_release_mem_region(resource_size_t start, resource_size_t n)
> +{
> + release_mem_region(start, n);
> +}
> 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..a287dc0898e0
> --- /dev/null
> +++ b/rust/kernel/io/mem.rs
> @@ -0,0 +1,98 @@
> +// 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::Resource;
> +use crate::io::Io;
> +use crate::io::IoRaw;
> +use crate::prelude::*;
> +
> +/// 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.
> +///
> +/// Whether `IoMem` represents an exclusive access to the underlying memory
> +/// region is determined by the caller at creation time, as overlapping access
> +/// may be needed in some cases.
> +///
> +/// # Invariants
> +///
> +/// `IoMem` always holds an `IoRaw` inststance that holds a valid pointer to the
> +/// start of the I/O memory mapped region.
> +pub struct IoMem<const SIZE: usize = 0, const EXCLUSIVE: bool = true> {
> + io: IoRaw<SIZE>,
> + res_start: u64,

Please use bindings::resource_size_t here to to be compatible with 32-bit architectures.

> +}
> +
> +impl<const SIZE: usize, const EXCLUSIVE: bool> IoMem<SIZE, EXCLUSIVE> {
> + /// Creates a new `IoMem` instance.
> + pub(crate) fn new(resource: &Resource, device: &Device) -> Result<Devres<Self>> {
> + let size = resource.size();
> + if size == 0 {
> + return Err(EINVAL);
> + }
> +
> + let res_start = resource.start();
> +
> + if EXCLUSIVE {
> + // SAFETY:
> + // - `res_start` and `size` are read from a presumably valid `struct resource`.
> + // - `size` is known not to be zero at this point.
> + // - `resource.name()` returns a valid C string.
> + let mem_region = unsafe {
> + bindings::request_mem_region(res_start, size, resource.name().as_char_ptr())
> + };
> +
> + if mem_region.is_null() {
> + return Err(EBUSY);
> + }
> + }
> +
> + // 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() {
> + if EXCLUSIVE {
> + // SAFETY:
> + // - `res_start` and `size` are read from a presumably valid `struct resource`.
> + // - `size` is the same as the one passed to `request_mem_region`.
> + unsafe { bindings::release_mem_region(res_start, size) };
> + }
> + return Err(ENOMEM);
> + }
> +
> + let io = IoRaw::new(addr as usize, size as usize)?;
> + let io = IoMem { io, res_start };
> + let devres = Devres::new(device, io, GFP_KERNEL)?;
> +
> + Ok(devres)
> + }
> +}
> +
> +impl<const SIZE: usize, const EXCLUSIVE: bool> Drop for IoMem<SIZE, EXCLUSIVE> {
> + fn drop(&mut self) {
> + if EXCLUSIVE {
> + // SAFETY: `res_start` and `io.maxsize()` were the values passed to
> + // `request_mem_region`.
> + unsafe { bindings::release_mem_region(self.res_start, self.io.maxsize() as u64) }

Please use bindings::resource_size_t here as well.

> + }
> +
> + // SAFETY: Safe as by the invariant of `Io`.
> + unsafe { bindings::iounmap(self.io.addr() as *mut core::ffi::c_void) }
> + }
> +}
> +
> +impl<const SIZE: usize, const EXCLUSIVE: bool> Deref for IoMem<SIZE, EXCLUSIVE> {
> + type Target = Io<SIZE>;
> +
> + fn deref(&self) -> &Self::Target {
> + // SAFETY: Safe as by the invariant of `IoMem`.
> + unsafe { Io::from_raw(&self.io) }
> + }
> +}

Cheers
Christian