rust: platform: add ioremap_resource and get_resource methods

This patch adds a logic similar to `devm_platform_ioremap_resource`
function adding:
  - `IoResource` enumerated type that groups the `IORESOURCE_*` macros.
  - `get_resource()` method that is a binding of `platform_get_resource`
  - `ioremap_resource` that is newly written method similar to
    `devm_platform_ioremap_resource`.

Signed-off-by: Maciej Falkowski <[email protected]>

Author: Maciej Falkowski

rust/kernel/io_mem.rs

@@ -9,6 +9,12 @@
 use crate::{bindings, Error, Result};
 use core::convert::TryInto;
 
+/// The type of `Resource`.
+pub enum IoResource {
+    /// i/o memory
+    Mem = bindings::IORESOURCE_MEM as _,
+}
+
 /// Represents a memory resource.
 pub struct Resource {
     offset: bindings::resource_size_t,

rust/kernel/platform.rs

@@ -10,7 +10,8 @@ use crate::{
     bindings, c_types,
     device::{self, RawDevice},
     driver,
-    error::{from_kernel_result, Result},
+    error::{from_kernel_result, Error, Result},
+    io_mem::{IoMem, IoResource, Resource},
     of,
     str::CStr,
     to_result,
@@ -180,6 +181,36 @@ impl Device {
         // SAFETY: By the type invariants, we know that `self.ptr` is non-null and valid.
         unsafe { (*self.ptr).id }
     }
+
+    /// Gets a system resources of a platform device.
+    pub fn get_resource(&self, rtype: IoResource, num: usize) -> Option<Resource> {
+        // SAFETY: `self.ptr` is valid by the type invariant.
+        let res = unsafe { bindings::platform_get_resource(self.ptr, rtype as _, num as _) };
+        if res.is_null() {
+            return None;
+        }
+
+        // SAFETY: The pointer `res` is returned from `bindings::platform_get_resource`
+        // above and checked if it is not a NULL.
+        unsafe { Resource::new((*res).start, (*res).end) }
+    }
+
+    /// Ioremaps resources of a platform device.
+    ///
+    /// # Safety
+    ///
+    /// Satisfy a safety requirements of the `IoMem<SIZE>::try_new` method.
+    /// Callers must ensure that either (a) the resulting interface cannot be used to initiate DMA
+    /// operations, or (b) that DMA operations initiated via the returned interface use DMA handles
+    /// allocated through the `dma` module.
+    pub fn ioremap_resource<const SIZE: usize>(&self, index: usize) -> Result<IoMem<SIZE>> {
+        if let Some(res) = self.get_resource(IoResource::Mem, index) {
+            // SAFETY: Valid by the safety contract.
+            unsafe { IoMem::<SIZE>::try_new(res) }
+        } else {
+            Err(Error::EINVAL)
+        }
+    }
 }
 
 // SAFETY: The device returned by `raw_device` is the raw platform device.