[PATCH v4 09/11] rust: device: expose the device DMA attribute

[Ke Sun via B4 Relay]

From: Sami Tolvanen <samitolvanen@xxxxxxxxxx>

A driver may need to know whether its device is DMA-coherent, but
rust/kernel exposes no accessor for the attribute today.

Add a transparent DmaAttr wrapper around device_get_dma_attr(), so all
three attribute values (unset, non-coherent, coherent) are covered, and
an is_coherent() accessor for the boolean case.

Signed-off-by: Sami Tolvanen <samitolvanen@xxxxxxxxxx>
[ Replace dma_coherent() with a DmaAttr wrapper covering all three
  attribute values. - Alvin ]
Co-developed-by: Alvin Sun <alvin.sun@xxxxxxxxx>
Signed-off-by: Alvin Sun <alvin.sun@xxxxxxxxx>
---
 rust/kernel/device.rs | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/rust/kernel/device.rs b/rust/kernel/device.rs
index 2291d85b6849e..d5bbebdf620df 100644
--- a/rust/kernel/device.rs
+++ b/rust/kernel/device.rs
@@ -260,6 +260,30 @@ pub unsafe fn drvdata_borrow<T>(&self) -> Pin<&T> {
     }
 }
 
+/// The DMA attribute of a device, as reported by firmware. A transparent
+/// wrapper around the kernel's `enum dev_dma_attr`, covering all its states.
+#[repr(transparent)]
+pub struct DmaAttr(bindings::dev_dma_attr);
+
+impl DmaAttr {
+    /// This wraps `device_get_dma_attr()` and only returns `true` for the
+    /// `DEV_DMA_COHERENT` attribute; no attribute or `DEV_DMA_NON_COHERENT` is non-coherent.
+    #[inline]
+    pub fn is_coherent(&self) -> bool {
+        self.0 == bindings::dev_dma_attr_DEV_DMA_COHERENT
+    }
+}
+
+impl Device<Bound> {
+    /// Returns the DMA attribute of the device as reported by firmware.
+    #[inline]
+    pub fn dma_attr(&self) -> DmaAttr {
+        // SAFETY: By the type invariants, `self.as_raw()` is a valid pointer
+        // to a `struct device`.
+        unsafe { DmaAttr(bindings::device_get_dma_attr(self.as_raw())) }
+    }
+}
+
 impl<Ctx: DeviceContext> Device<Ctx> {
     /// Obtain the raw `struct device *`.
     pub(crate) fn as_raw(&self) -> *mut bindings::device {

-- 
2.43.0