Message-ID: <aCYVG-VVdJXYnSTt@pollux>
Date: Thu, 15 May 2025 18:23:55 +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>,
	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>,
	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>,
	linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org
Subject: Re: [PATCH v8 3/3] rust: platform: allow ioremap of platform
 resources

On Fri, May 09, 2025 at 05:29:48PM -0300, Daniel Almeida wrote:
> +impl Device<device::Core> {
> +    /// Maps a platform resource through ioremap() where the size is known at
> +    /// compile time.
> +    ///
> +    /// # Examples
> +    ///
> +    /// ```no_run
> +    /// # use kernel::{bindings, c_str, platform};
> +    /// # use kernel::device::Core;
> +    ///
> +    ///
> +    /// fn probe(pdev: &mut platform::Device<Core>, /* ... */) -> Result<()> {

Should be &platform::Device<Core> (i.e. not mutable). You should also be able to
just use `Result` as return type. Though, it would probably be better to use the
real probe() function here, i.e.

	# struct Driver;

	impl platform::Driver for SampleDriver {
	   # type IdInfo = ();
	   # const OF_ID_TABLE: Option<of::IdTable<Self::IdInfo>> = None;

	   fn probe(
	      pdev: &platform::Device<Core>,
	      info: Option<&Self::IdInfo>,
	   ) -> Result<Pin<KBox<Self>>> {
	      ...
	   }
	}

> +    ///     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)?.read32_relaxed(offset);
> +    ///
> +    ///     iomem.try_access().ok_or(ENODEV)?.write32_relaxed(data, offset);

Since this won't land for v6.16, can you please use Devres::access() [1]
instead? I.e.

	let iomem = pdev.ioremap_resource_sized::<42>(&resource)?;
	let io = Devres::access(pdev.as_ref())?;

	let data = io.read32_relaxed(offset);
	io.write32_relaxed(data, offset);

Devres::access() is in nova-next and lands in v6.16.

[1] https://gitlab.freedesktop.org/drm/nova/-/commit/f301cb978c068faa8fcd630be2cb317a2d0ec063

> +    ///
> +    ///     # Ok::<(), Error>(())
> +    /// }
> +    /// ```
> +    pub fn ioremap_resource_sized<const SIZE: usize>(
> +        &self,
> +        resource: &Resource,
> +    ) -> Result<Devres<IoMem<SIZE>>> {
> +        IoMem::new(resource, self.as_ref())
> +    }
> +
> +    /// Same as [`Self::ioremap_resource_sized`] but with exclusive access to the
> +    /// underlying region.
> +    pub fn ioremap_resource_exclusive_sized<const SIZE: usize>(
> +        &self,
> +        resource: &Resource,
> +    ) -> Result<Devres<ExclusiveIoMem<SIZE>>> {
> +        ExclusiveIoMem::new(resource, self.as_ref())
> +    }
> +
> +    /// Maps a platform resource through ioremap().
> +    ///
> +    /// # Examples
> +    ///
> +    /// ```no_run
> +    /// # use kernel::{bindings, c_str, platform};
> +    /// # use kernel::device::Core;
> +    ///
> +    /// fn probe(pdev: &mut platform::Device<Core>, /* ... */) -> Result<()> {
> +    ///     let offset = 0; // Some offset.
> +    ///
> +    ///     // Unlike `ioremap_resource_sized`, here the size of the memory region
> +    ///     // is not known at compile time, so only the `try_read*` and `try_write*`
> +    ///     // family of functions should be used, leading to runtime checks on every
> +    ///     // access.
> +    ///     let resource = pdev.resource(0).ok_or(ENODEV)?;
> +    ///     let iomem = pdev.ioremap_resource(&resource)?;
> +    ///
> +    ///     let data = iomem.try_access().ok_or(ENODEV)?.try_read32_relaxed(offset)?;
> +    ///
> +    ///     iomem.try_access().ok_or(ENODEV)?.try_write32_relaxed(data, offset)?;
> +    ///
> +    ///     # Ok::<(), Error>(())
> +    /// }

Same as above.

> +    /// ```
> +    pub fn ioremap_resource(&self, resource: &Resource) -> Result<Devres<IoMem<0>>> {
> +        self.ioremap_resource_sized::<0>(resource)
> +    }
> +
> +    /// Same as [`Self::ioremap_resource`] but with exclusive access to the underlying
> +    /// region.
> +    pub fn ioremap_resource_exclusive(
> +        &self,
> +        resource: &Resource,
> +    ) -> Result<Devres<ExclusiveIoMem<0>>> {
> +        self.ioremap_resource_exclusive_sized::<0>(resource)
> +    }
> +
> +    /// Returns the resource at `index`, if any.
> +    pub fn resource(&self, index: u32) -> Option<&Resource> {
> +        // SAFETY: `self.as_raw()` returns a valid pointer to a `struct platform_device`.
> +        let resource = unsafe {
> +            bindings::platform_get_resource(self.as_raw(), bindings::IORESOURCE_MEM, index)
> +        };
> +
> +        if resource.is_null() {
> +            return None;
> +        }
> +
> +        // SAFETY: `resource` is a valid pointer to a `struct resource` as
> +        // returned by `platform_get_resource`.
> +        Some(unsafe { Resource::from_ptr(resource) })
> +    }
> +
> +    /// Returns the resource with a given `name`, if any.
> +    pub fn resource_by_name(&self, name: &CStr) -> Option<&Resource> {

This method should be a separate patch, no? Also, I think this one can go into
the `impl<Ctx: device::DeviceContext> Device<Ctx>` block, since it should be
valid to call from any device context.

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