rust: platform: add resource accessors

The previous patches have added the abstractions for Resources and the
ability to map them and therefore read and write the underlying memory .

The only thing missing to make this accessible for platform devices is
to provide accessors that return instances of IoRequest<'a>. These
ensure that the resource are valid only for the lifetime of the platform
device, and that the platform device is in the Bound state.

Therefore, add these accessors. Also make it possible to retrieve
resources from platform devices in Rust using either a name or an index.

Acked-by: Miguel Ojeda <ojeda@kernel.org>
Signed-off-by: Daniel Almeida <daniel.almeida@collabora.com>
Link: https://lore.kernel.org/r/20250717-topics-tyr-platform_iomem-v15-3-beca780b77e3@collabora.com
[ Remove #[expect(dead_code)] from IoRequest::new() and move SAFETY
  comments right on top of unsafe blocks to avoid clippy warnings for
  some (older) clippy versions. - Danilo ]
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

rust/kernel/io/mem.rs

@@ -28,7 +28,6 @@ impl<'a> IoRequest<'a> {
     ///
     /// Callers must ensure that `resource` is valid for `device` during the
     /// lifetime `'a`.
-    #[expect(dead_code)]
     pub(crate) unsafe fn new(device: &'a Device<Bound>, resource: &'a Resource) -> Self {
         IoRequest { device, resource }
     }

rust/kernel/platform.rs

@@ -5,8 +5,11 @@
 //! C header: [`include/linux/platform_device.h`](srctree/include/linux/platform_device.h)
 
 use crate::{
-    acpi, bindings, container_of, device, driver,
+    acpi, bindings, container_of,
+    device::{self, Bound},
+    driver,
     error::{from_result, to_result, Result},
+    io::{mem::IoRequest, Resource},
     of,
     prelude::*,
     types::Opaque,
@@ -224,6 +227,61 @@ impl<Ctx: device::DeviceContext> Device<Ctx> {
     fn as_raw(&self) -> *mut bindings::platform_device {
         self.0.get()
     }
+
+    /// Returns the resource at `index`, if any.
+    pub fn resource_by_index(&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_raw(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(),
+            )
+        };
+
+        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_raw(resource) })
+    }
+}
+
+impl Device<Bound> {
+    /// Returns an `IoRequest` for the resource at `index`, if any.
+    pub fn io_request_by_index(&self, index: u32) -> Option<IoRequest<'_>> {
+        self.resource_by_index(index)
+            // SAFETY: `resource` is a valid resource for `&self` during the
+            // lifetime of the `IoRequest`.
+            .map(|resource| unsafe { IoRequest::new(self.as_ref(), resource) })
+    }
+
+    /// Returns an `IoRequest` for the resource with a given `name`, if any.
+    pub fn io_request_by_name(&self, name: &CStr) -> Option<IoRequest<'_>> {
+        self.resource_by_name(name)
+            // SAFETY: `resource` is a valid resource for `&self` during the
+            // lifetime of the `IoRequest`.
+            .map(|resource| unsafe { IoRequest::new(self.as_ref(), resource) })
+    }
 }
 
 // SAFETY: `Device` is a transparent wrapper of a type that doesn't depend on `Device`'s generic