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

[Daniel Almeida <daniel.almeida@collabora.com>]

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) }?;
+        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