linux-kernel - Re: [PATCH v12 2/3] rust: io: mem: add a generic iomem abstraction

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Message-ID: <aGlfzdUjvSkdFhNz@cassiopeiae>
Date: Sat, 5 Jul 2025 19:24:29 +0200
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>,
	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>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Ying Huang <huang.ying.caritas@...il.com>,
	Benno Lossin <lossin@...nel.org>, linux-kernel@...r.kernel.org,
	rust-for-linux@...r.kernel.org
Subject: Re: [PATCH v12 2/3] rust: io: mem: add a generic iomem abstraction

On Fri, Jul 04, 2025 at 01:25:27PM -0300, Daniel Almeida wrote:

This looks good now, one comment below.

> +    /// Creates a new `IoMem` instance from a previously acquired [`IoRequest`].
> +    pub fn new<'a>(io_request: IoRequest<'a>) -> Result<impl PinInit<Devres<Self>, Error> + 'a> {
> +        let io = Self::ioremap(io_request.resource)?;
> +        let devres = Devres::new(io_request.device, io);
> +
> +        Ok(devres)
> +    }

This method should not return `Result<impl PinInit<Devres<Self>, Error> + 'a>`,
but just `impl PinInit<Devres<Self>, Error> + 'a`.

Here's the full diff of the changes needed. :)

diff --git a/rust/kernel/io/mem.rs b/rust/kernel/io/mem.rs
index b047b9a73ae5..cb0805ef0860 100644
--- a/rust/kernel/io/mem.rs
+++ b/rust/kernel/io/mem.rs
@@ -60,7 +60,7 @@ pub(crate) unsafe fn new(device: &'a Device<Bound>, resource: &'a Resource) -> S
     ///       //
     ///       // No runtime checks will apply when reading and writing.
     ///       let request = pdev.request_io_by_index(0).ok_or(ENODEV)?;
-    ///       let iomem = request.iomap_sized::<42>()?;
+    ///       let iomem = request.iomap_sized::<42>();
     ///       let iomem = KBox::pin_init(iomem, GFP_KERNEL)?;
     ///
     ///       let io = iomem.access(pdev.as_ref())?;
@@ -74,9 +74,7 @@ pub(crate) unsafe fn new(device: &'a Device<Bound>, resource: &'a Resource) -> S
     ///     }
     /// }
     /// ```
-    pub fn iomap_sized<const SIZE: usize>(
-        self,
-    ) -> Result<impl PinInit<Devres<IoMem<SIZE>>, Error> + 'a> {
+    pub fn iomap_sized<const SIZE: usize>(self) -> impl PinInit<Devres<IoMem<SIZE>>, Error> + 'a {
         IoMem::new(self)
     }

@@ -88,7 +86,7 @@ pub fn iomap_sized<const SIZE: usize>(
     /// C API.
     pub fn iomap_exclusive_sized<const SIZE: usize>(
         self,
-    ) -> Result<impl PinInit<Devres<ExclusiveIoMem<SIZE>>, Error> + 'a> {
+    ) -> impl PinInit<Devres<ExclusiveIoMem<SIZE>>, Error> + 'a {
         ExclusiveIoMem::new(self)
     }

@@ -122,7 +120,7 @@ pub fn iomap_exclusive_sized<const SIZE: usize>(
     ///       // family of functions should be used, leading to runtime checks on every
     ///       // access.
     ///       let request = pdev.request_io_by_index(0).ok_or(ENODEV)?;
-    ///       let iomem = request.iomap()?;
+    ///       let iomem = request.iomap();
     ///       let iomem = KBox::pin_init(iomem, GFP_KERNEL)?;
     ///
     ///       let io = iomem.access(pdev.as_ref())?;
@@ -135,13 +133,13 @@ pub fn iomap_exclusive_sized<const SIZE: usize>(
     ///     }
     /// }
     /// ```
-    pub fn iomap(self) -> Result<impl PinInit<Devres<IoMem<0>>, Error> + 'a> {
+    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) -> Result<impl PinInit<Devres<ExclusiveIoMem<0>>, Error> + 'a> {
+    pub fn iomap_exclusive(self) -> impl PinInit<Devres<ExclusiveIoMem<0>>, Error> + 'a {
         Self::iomap_exclusive_sized::<0>(self)
     }
 }
@@ -185,11 +183,11 @@ fn ioremap(resource: &Resource) -> Result<Self> {
     }

     /// Creates a new `ExclusiveIoMem` instance from a previously acquired [`IoRequest`].
-    pub fn new<'a>(io_request: IoRequest<'a>) -> Result<impl PinInit<Devres<Self>, Error> + 'a> {
-        let iomem = Self::ioremap(io_request.resource)?;
-        let devres = Devres::new(io_request.device, iomem);
+    pub fn new<'a>(io_request: IoRequest<'a>) -> impl PinInit<Devres<Self>, Error> + 'a {
+        let dev = io_request.device;
+        let res = io_request.resource;

-        Ok(devres)
+        Devres::new(dev, Self::ioremap(res))
     }
 }

@@ -249,11 +247,11 @@ fn ioremap(resource: &Resource) -> Result<Self> {
     }

     /// Creates a new `IoMem` instance from a previously acquired [`IoRequest`].
-    pub fn new<'a>(io_request: IoRequest<'a>) -> Result<impl PinInit<Devres<Self>, Error> + 'a> {
-        let io = Self::ioremap(io_request.resource)?;
-        let devres = Devres::new(io_request.device, io);
+    pub fn new<'a>(io_request: IoRequest<'a>) -> impl PinInit<Devres<Self>, Error> + 'a {
+        let dev = io_request.device;
+        let res = io_request.resource;

-        Ok(devres)
+        Devres::new(dev, Self::ioremap(res))
     }
 }