Re: [PATCH v7 3/3] rust: platform: allow ioremap of platform resources

Danilo Krummrich
2025-03-18T17:43:28Z

Hi Daniel,

On Tue, Mar 18, 2025 at 02:20:43PM -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, 122 insertions(+), 1 deletion(-)

You need to rebase this onto driver-core-next.

>
> diff --git a/rust/kernel/platform.rs b/rust/kernel/platform.rs
> index 1297f5292ba9b7ca9784f84979efbeccb0768bd3..56f3d7c0d536d77082d7f8d2407de17ee3e95ffa 100644
> --- a/rust/kernel/platform.rs
> +++ b/rust/kernel/platform.rs
> @@ -5,8 +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::{
> + mem::{ExclusiveIoMem, IoMem},
> + resource::Resource,
> + },
> of,
> prelude::*,
> str::CStr,
> @@ -191,6 +197,121 @@ fn as_raw(&self) -> *mut bindings::platform_device {
> // embedded in `struct platform_device`.
> unsafe { container_of!(self.0.as_raw(), bindings::platform_device, dev) }.cast_mut()
> }
> +
> + /// Maps a platform resource through ioremap() where the size is known at
> + /// compile time.
> + ///
> + /// # Examples
> + ///
> + /// ```no_run
> + /// use kernel::{bindings, c_str, platform};
> + ///
> + /// fn probe(pdev: &mut platform::Device, /* ... */) -> Result<()> {
> + /// let offset = 0; // Some offset.
> + ///
> + /// // If the size is known at compile time, use `ioremap_resource_sized`.
> + /// // No runtime checks will apply when reading and writing.
> + /// let resource = pdev.resource(0).ok_or(ENODEV)?;
> + /// let iomem = pdev.ioremap_resource_sized::<42>(&resource)?;
> + ///
> + /// // 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 = iomem.try_access().ok_or(ENODEV)?.readl(offset);
> + ///
> + /// iomem.try_access().ok_or(ENODEV)?.writel(data, offset);

I'd probably write this as

|| -> Result {
let iomem = iomem.try_access().ok_or(ENODEV)?;

iomem.read32(offset);
iomem.write32(data, offset);

Ok(())
}()?;

There's also a patch [1] in progress that makes this more convenient.

[1] https://lore.kernel.org/rust-for-linux/20250313-try_with-v1-1-adcae7ed98a9@nvidia.com/