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

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Message-ID: <Z9mwu-RHwZ8qwcbH@cassiopeiae>
Date: Tue, 18 Mar 2025 18:43:23 +0100
From: Danilo Krummrich <dakr@...nel.org>
To: Daniel Almeida <daniel.almeida@...labora.com>
Cc: Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>,
	Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Benno Lossin <benno.lossin@...ton.me>,
	Andreas Hindborg <a.hindborg@...nel.org>,
	Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org
Subject: Re: [PATCH v7 3/3] rust: platform: allow ioremap of platform
 resources

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@...labora.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/