Rust: io: Add memcpy_fromio wrapper

Adapted from
*RFL import: kernel::io_mem

Commit reference: 3dfc5eb

Signed-off-by: Janne Grunau <j@jannau.net>

Author: hoshinolina

rust/helpers/io.c

@@ -18,6 +18,11 @@ void rust_helper_iounmap(void __iomem *addr)
 	iounmap(addr);
 }
 
+void rust_helper_memcpy_fromio(void *to, const void __iomem *from, long count)
+{
+	memcpy_fromio(to, from, count);
+}
+
 u8 rust_helper_readb(const void __iomem *addr)
 {
 	return readb(addr);

rust/kernel/io.rs

@@ -203,6 +203,15 @@ impl<const SIZE: usize> Io<SIZE> {
         }
     }
 
+    #[inline]
+    const fn length_valid(offset: usize, length: usize, size: usize) -> bool {
+        if let Some(end) = offset.checked_add(length) {
+            end <= size
+        } else {
+            false
+        }
+    }
+
     #[inline]
     fn io_addr<U>(&self, offset: usize) -> Result<usize> {
         if !Self::offset_valid::<U>(offset, self.maxsize()) {
@@ -221,6 +230,46 @@ impl<const SIZE: usize> Io<SIZE> {
         self.addr() + offset
     }
 
+    /// Copy memory block from an i/o memory by filling the specified buffer with it.
+    ///
+    /// # Examples
+    /// ```
+    /// use kernel::io::mem::IoMem;
+    /// use kernel::io::mem::Resource;
+    ///
+    /// fn test(device: &Device, res: Resource) -> Result {
+    ///     // Create an i/o memory block of at least 100 bytes.
+    ///     let devres_mem = IoMem::<100>::new(res, device)?;
+    ///     // aquire access to memory block
+    ///     let mem = devres_mem.try_access()?;
+    ///
+    ///     let mut buffer: [u8; 32] = [0; 32];
+    ///
+    ///     // Memcpy 16 bytes from an offset 10 of i/o memory block into the buffer.
+    ///     mem.try_memcpy_fromio(&mut buffer[..16], 10)?;
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn try_memcpy_fromio(&self, buffer: &mut [u8], offset: usize) -> Result {
+        if buffer.len() == 0 || !Self::length_valid(offset, buffer.len(), self.maxsize()) {
+            return Err(EINVAL);
+        }
+        let addr = self.io_addr::<crate::ffi::c_char>(offset)?;
+
+        // SAFETY:
+        //   - The type invariants guarantee that `adr` is a valid pointer.
+        //   - The bounds of `buffer` are checked with a call to `length_valid`.
+        unsafe {
+            bindings::memcpy_fromio(
+                buffer.as_mut_ptr() as *mut _,
+                addr as *const _,
+                buffer.len() as _,
+            )
+        };
+        Ok(())
+    }
+
     define_read!(read8, try_read8, readb -> u8);
     define_read!(read16, try_read16, readw -> u16);
     define_read!(read32, try_read32, readl -> u32);