[PATCH v8 07/10] rust: io: introduce `IntoIoVal` trait and single-argument `write_val`

[Alexandre Courbot <acourbot@nvidia.com>]

Some I/O types, like fixed address registers, carry their location
alongside their values. For these types, the regular `Io::write` method
can lead into repeating the location information twice: once to provide
the location itself, another time to build the value.

Add a new `Io::write_val` convenience method that takes a single
argument implementing `IntoIoVal`, a trait that decomposes implementors
into a `(location, value)` tuple. This allows write operations on fixed
offset registers to be done while specifying their name only once.

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
---
 rust/kernel/io.rs | 68 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 68 insertions(+)

diff --git a/rust/kernel/io.rs b/rust/kernel/io.rs
index ed6fab001a39..09a0fe06f201 100644
--- a/rust/kernel/io.rs
+++ b/rust/kernel/io.rs
@@ -216,6 +216,22 @@ fn offset(&self) -> usize {
 // Provide the ability to read any primitive type from a [`usize`].
 impl_usize_ioloc!(u8, u16, u32, u64);
 
+/// Trait implemented by items that contain both an I/O location and a value to assign to it.
+///
+/// Implementors can be used with [`Io::write_val`].
+pub trait IntoIoVal<T, L: IoLoc<T>> {
+    /// Consumes `self` and returns a `(location, value)` tuple describing a valid I/O write
+    /// operation.
+    fn into_io_val(self) -> (L, T);
+}
+
+/// `(location, value)` tuples can be used as [`IntoIoVal`]s.
+impl<T, L: IoLoc<T>> IntoIoVal<T, L> for (L, T) {
+    fn into_io_val(self) -> (L, T) {
+        self
+    }
+}
+
 /// Types implementing this trait (e.g. MMIO BARs or PCI config regions)
 /// can perform I/O operations on regions of memory.
 ///
@@ -463,6 +479,32 @@ fn try_write<T, L>(&self, location: L, value: T) -> Result
         Ok(())
     }
 
+    /// Generic fallible write of value bearing its location, with runtime bounds check.
+    ///
+    /// # Examples
+    ///
+    /// Tuples carrying a location and a value can be used with this method:
+    ///
+    /// ```no_run
+    /// use kernel::io::{Io, Mmio};
+    ///
+    /// fn do_writes(io: &Mmio) -> Result {
+    ///     // 32-bit write of value `1` at address `0x10`.
+    ///     io.try_write_val((0x10, 1u32))
+    /// }
+    /// ```
+    #[inline(always)]
+    fn try_write_val<T, L, V>(&self, value: V) -> Result
+    where
+        L: IoLoc<T>,
+        V: IntoIoVal<T, L>,
+        Self: IoCapable<L::IoType>,
+    {
+        let (location, value) = value.into_io_val();
+
+        self.try_write(location, value)
+    }
+
     /// Generic fallible update with runtime bounds check.
     ///
     /// Caution: this does not perform any synchronization. Race conditions can occur in case of
@@ -559,6 +601,32 @@ fn write<T, L>(&self, location: L, value: T)
         unsafe { self.io_write(io_value, address) }
     }
 
+    /// Generic infallible write of value bearing its location, with compile-time bounds check.
+    ///
+    /// # Examples
+    ///
+    /// Tuples carrying a location and a value can be used with this method:
+    ///
+    /// ```no_run
+    /// use kernel::io::{Io, Mmio};
+    ///
+    /// fn do_writes(io: &Mmio) {
+    ///     // 32-bit write of value `1` at address `0x10`.
+    ///     io.write_val((0x10, 1u32));
+    /// }
+    /// ```
+    #[inline(always)]
+    fn write_val<T, L, V>(&self, value: V)
+    where
+        L: IoLoc<T>,
+        V: IntoIoVal<T, L>,
+        Self: IoKnownSize + IoCapable<L::IoType>,
+    {
+        let (location, value) = value.into_io_val();
+
+        self.write(location, value)
+    }
+
     /// Generic infallible update with compile-time bounds check.
     ///
     /// Caution: this does not perform any synchronization. Race conditions can occur in case of

-- 
2.53.0