[PATCH v2 2/5] rust: dma: add DMA addressing capabilities

[Danilo Krummrich <dakr@kernel.org>]

Implement `dma_set_mask()`, `dma_set_coherent_mask()` and
`dma_set_mask_and_coherent()` in the `dma::Device` trait.

Those methods are used to set up the device's DMA addressing
capabilities.

Reviewed-by: Abdiel Janulgue <abdiel.janulgue@gmail.com>
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/helpers/dma.c |   5 ++
 rust/kernel/dma.rs | 112 +++++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 113 insertions(+), 4 deletions(-)

diff --git a/rust/helpers/dma.c b/rust/helpers/dma.c
index df8b8a77355a..6e741c197242 100644
--- a/rust/helpers/dma.c
+++ b/rust/helpers/dma.c
@@ -14,3 +14,8 @@ void rust_helper_dma_free_attrs(struct device *dev, size_t size, void *cpu_addr,
 {
 	dma_free_attrs(dev, size, cpu_addr, dma_handle, attrs);
 }
+
+int rust_helper_dma_set_mask_and_coherent(struct device *dev, u64 mask)
+{
+	return dma_set_mask_and_coherent(dev, mask);
+}
diff --git a/rust/kernel/dma.rs b/rust/kernel/dma.rs
index f0af23d08e8d..afd3ba538e3c 100644
--- a/rust/kernel/dma.rs
+++ b/rust/kernel/dma.rs
@@ -6,9 +6,9 @@
 
 use crate::{
     bindings, build_assert, device,
-    device::Bound,
-    error::code::*,
-    error::Result,
+    device::{Bound, Core},
+    error::{to_result, Result},
+    prelude::*,
     transmute::{AsBytes, FromBytes},
     types::ARef,
 };
@@ -18,7 +18,111 @@
 /// The [`dma::Device`](Device) trait should be implemented by bus specific device representations,
 /// where the underlying bus is DMA capable, such as [`pci::Device`](::kernel::pci::Device) or
 /// [`platform::Device`](::kernel::platform::Device).
-pub trait Device: AsRef<device::Device<Core>> {}
+pub trait Device: AsRef<device::Device<Core>> {
+    /// Set up the device's DMA streaming addressing capabilities.
+    ///
+    /// This method is usually called once from `probe()` as soon as the device capabilities are
+    /// known.
+    ///
+    /// # Safety
+    ///
+    /// This method must not be called concurrently with any DMA allocation or mapping primitives,
+    /// such as [`CoherentAllocation::alloc_attrs`].
+    unsafe fn dma_set_mask(&self, mask: DmaMask) -> Result {
+        // SAFETY:
+        // - By the type invariant of `device::Device`, `self.as_ref().as_raw()` is valid.
+        // - The safety requirement of this function guarantees that there are no concurrent calls
+        //   to DMA allocation and mapping primitives using this mask.
+        to_result(unsafe { bindings::dma_set_mask(self.as_ref().as_raw(), mask.value()) })
+    }
+
+    /// Set up the device's DMA coherent addressing capabilities.
+    ///
+    /// This method is usually called once from `probe()` as soon as the device capabilities are
+    /// known.
+    ///
+    /// # Safety
+    ///
+    /// This method must not be called concurrently with any DMA allocation or mapping primitives,
+    /// such as [`CoherentAllocation::alloc_attrs`].
+    unsafe fn dma_set_coherent_mask(&self, mask: DmaMask) -> Result {
+        // SAFETY:
+        // - By the type invariant of `device::Device`, `self.as_ref().as_raw()` is valid.
+        // - The safety requirement of this function guarantees that there are no concurrent calls
+        //   to DMA allocation and mapping primitives using this mask.
+        to_result(unsafe { bindings::dma_set_coherent_mask(self.as_ref().as_raw(), mask.value()) })
+    }
+
+    /// Set up the device's DMA addressing capabilities.
+    ///
+    /// This is a combination of [`Device::dma_set_mask`] and [`Device::dma_set_coherent_mask`].
+    ///
+    /// This method is usually called once from `probe()` as soon as the device capabilities are
+    /// known.
+    ///
+    /// # Safety
+    ///
+    /// This method must not be called concurrently with any DMA allocation or mapping primitives,
+    /// such as [`CoherentAllocation::alloc_attrs`].
+    unsafe fn dma_set_mask_and_coherent(&self, mask: DmaMask) -> Result {
+        // SAFETY:
+        // - By the type invariant of `device::Device`, `self.as_ref().as_raw()` is valid.
+        // - The safety requirement of this function guarantees that there are no concurrent calls
+        //   to DMA allocation and mapping primitives using this mask.
+        to_result(unsafe {
+            bindings::dma_set_mask_and_coherent(self.as_ref().as_raw(), mask.value())
+        })
+    }
+}
+
+/// A DMA mask that holds a bitmask with the lowest `n` bits set.
+///
+/// Use [`DmaMask::new`] to construct a value. Values are guaranteed to
+/// never exceed the bit width of `u64`.
+///
+/// This is the Rust equivalent of the C macro `DMA_BIT_MASK()`.
+///
+/// # Examples
+///
+/// ```
+/// use kernel::dma::DmaMask;
+///
+/// let mask0 = DmaMask::new(0)?;
+/// assert_eq!(mask0.value(), 0);
+///
+/// let mask1 = DmaMask::new(1)?;
+/// assert_eq!(mask1.value(), 0b1);
+///
+/// let mask64 = DmaMask::new(64)?;
+/// assert_eq!(mask64.value(), u64::MAX);
+///
+/// let mask_overflow = DmaMask::new(100);
+/// assert!(mask_overflow.is_err());
+/// # Ok::<(), Error>(())
+/// ```
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct DmaMask(u64);
+
+impl DmaMask {
+    /// Constructs a `DmaMask` with the lowest `n` bits set to `1`.
+    ///
+    /// For `n <= 64`, sets exactly the lowest `n` bits.
+    /// For `n > 64`, returns [`EINVAL`].
+    #[inline]
+    pub const fn new(n: usize) -> Result<Self> {
+        Ok(Self(match n {
+            0 => 0,
+            1..=64 => u64::MAX >> (64 - n),
+            _ => return Err(EINVAL),
+        }))
+    }
+
+    /// Returns the underlying `u64` bitmask value.
+    #[inline]
+    pub const fn value(&self) -> u64 {
+        self.0
+    }
+}
 
 /// Possible attributes associated with a DMA mapping.
 ///
-- 
2.50.0