Re: [PATCH v4 3/3] rust: platform: allow ioremap of platform resources

[Danilo Krummrich <dakr@kernel.org>]

On Thu, Jan 09, 2025 at 10:30:55AM -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 a 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 | 98 ++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 97 insertions(+), 1 deletion(-)
> 
> diff --git a/rust/kernel/platform.rs b/rust/kernel/platform.rs
> index 03287794f9d0..9575917a1b2d 100644
> --- a/rust/kernel/platform.rs
> +++ b/rust/kernel/platform.rs
> @@ -5,8 +5,11 @@
>  //! 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::IoMem, resource::Resource},
>      of,
>      prelude::*,
>      str::CStr,
> @@ -189,6 +192,99 @@ 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, true)?;
> +    ///
> +    ///     // 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);
> +    ///
> +    ///     # Ok::<(), Error>(())
> +    /// }
> +    /// ```
> +    pub fn ioremap_resource_sized<const SIZE: usize>(
> +        &self,
> +        resource: &Resource,
> +        exclusive: bool,
> +    ) -> Result<Devres<IoMem<SIZE>>> {
> +        // SAFETY: We wrap the resulting `IoMem` in a `Devres`.
> +        let io = unsafe { IoMem::new(resource, exclusive) }?;

If we trust `resource`, then IoMem::new() could already return a `Devres<IoMem>`
avoiding the `unsafe`.

> +        let devres = Devres::new(self.as_ref(), io, GFP_KERNEL)?;
> +
> +        Ok(devres)
> +    }
> +
> +    /// Maps a platform resource through ioremap().
> +    ///
> +    /// # Examples
> +    ///
> +    /// ```no_run
> +    /// # use kernel::{bindings, c_str, platform};
> +    ///
> +    /// fn probe(pdev: &mut platform::Device, /* ... */) -> 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 are exposed, leading to runtime checks on every
> +    ///     // access.
> +    ///     let iomem = pdev.ioremap_resource(&resource, true)?;
> +    ///
> +    ///     let data = iomem.try_access().ok_or(ENODEV)?.try_readl(offset)?;
> +    ///
> +    ///     iomem.try_access().ok_or(ENODEV)?.try_writel(data, offset)?;
> +    ///
> +    ///     # Ok::<(), Error>(())
> +    /// }
> +    /// ```
> +    pub fn ioremap_resource(&self, resource: &Resource, exclusive: bool) -> Result<Devres<IoMem>> {
> +        self.ioremap_resource_sized::<0>(resource, exclusive)
> +    }
> +
> +    /// 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)
> +        };
> +
> +        // SAFETY: `resource` is a valid pointer to a `struct resource` as
> +        // returned by `platform_get_resource`.
> +        (!resource.is_null()).then(|| unsafe { Resource::from_ptr(resource) })
> +    }
> +
> +    /// Returns the resource with a given `name`, if any.
> +    pub fn resource_by_name(&self, name: &CStr) -> Option<&Resource> {
> +        // SAFETY: `self.as_raw()` returns a valid pointer to a `struct
> +        // platform_device` and `name` points to a valid C string.
> +        let resource = unsafe {
> +            bindings::platform_get_resource_byname(
> +                self.as_raw(),
> +                bindings::IORESOURCE_MEM,
> +                name.as_char_ptr(),
> +            )
> +        };
> +
> +        // SAFETY: `resource` is a valid pointer to a `struct resource` as
> +        // returned by `platform_get_resource`.
> +        (!resource.is_null()).then(|| unsafe { Resource::from_ptr(resource) })
> +    }
>  }
>  
>  impl AsRef<device::Device> for Device {
> -- 
> 2.47.1
>