linux-kernel - [PATCH v14 06/11] rust: dma: add dma addressing capabilities

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Message-ID: <20250311174930.2348813-7-abdiel.janulgue@gmail.com>
Date: Tue, 11 Mar 2025 19:48:02 +0200
From: Abdiel Janulgue <abdiel.janulgue@...il.com>
To: rust-for-linux@...r.kernel.org,
	daniel.almeida@...labora.com,
	dakr@...nel.org,
	robin.murphy@....com,
	aliceryhl@...gle.com
Cc: Miguel Ojeda <ojeda@...nel.org>,
	Alex Gaynor <alex.gaynor@...il.com>,
	Boqun Feng <boqun.feng@...il.com>,
	Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Benno Lossin <benno.lossin@...ton.me>,
	Andreas Hindborg <a.hindborg@...nel.org>,
	Trevor Gross <tmgross@...ch.edu>,
	Valentin Obst <kernel@...entinobst.de>,
	linux-kernel@...r.kernel.org (open list),
	Christoph Hellwig <hch@....de>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	airlied@...hat.com,
	iommu@...ts.linux.dev (open list:DMA MAPPING HELPERS),
	Abdiel Janulgue <abdiel.janulgue@...il.com>
Subject: [PATCH v14 06/11] rust: dma: add dma addressing capabilities

From: Danilo Krummrich <dakr@...nel.org>

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

Those methods are used to inform the kernel about the device's DMA
addressing capabilities.

Co-developed-by: Abdiel Janulgue <abdiel.janulgue@...il.com>
Signed-off-by: Abdiel Janulgue <abdiel.janulgue@...il.com>
Signed-off-by: Danilo Krummrich <dakr@...nel.org>
---
 rust/helpers/dma.c     |  8 ++++++++
 rust/helpers/helpers.c |  1 +
 rust/kernel/dma.rs     | 46 +++++++++++++++++++++++++++++++++++++++---
 3 files changed, 52 insertions(+), 3 deletions(-)
 create mode 100644 rust/helpers/dma.c

diff --git a/rust/helpers/dma.c b/rust/helpers/dma.c
new file mode 100644
index 000000000000..8eb482386f93
--- /dev/null
+++ b/rust/helpers/dma.c
@@ -0,0 +1,8 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/dma-mapping.h>
+
+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/helpers/helpers.c b/rust/helpers/helpers.c
index 0640b7e115be..8f3808c8b7fe 100644
--- a/rust/helpers/helpers.c
+++ b/rust/helpers/helpers.c
@@ -13,6 +13,7 @@
 #include "build_bug.c"
 #include "cred.c"
 #include "device.c"
+#include "dma.c"
 #include "err.c"
 #include "fs.c"
 #include "io.c"
diff --git a/rust/kernel/dma.rs b/rust/kernel/dma.rs
index 7ff797a7ad18..ac3ec0042327 100644
--- a/rust/kernel/dma.rs
+++ b/rust/kernel/dma.rs
@@ -5,10 +5,10 @@
 //! C header: [`include/linux/dma-mapping.h`](srctree/include/linux/dma-mapping.h)
 
 use crate::{
-    bindings, build_assert,
-    device,
+    bindings, build_assert, device,
     error::code::*,
     error::Result,
+    prelude::*,
     transmute::{AsBytes, FromBytes},
     types::ARef,
 };
@@ -18,7 +18,35 @@
 /// The [`Device`] trait should be implemented by bus specific device representations, where the
 /// underlying bus has potential support for DMA, such as [`crate::pci::Device`] or
 /// [crate::platform::Device].
-pub trait Device: AsRef<device::Device> {}
+pub trait Device: AsRef<device::Device> {
+    /// Inform the kernel about the device's DMA addressing capabilities.
+    ///
+    /// Set both the DMA mask and the coherent DMA mask to the same value.
+    ///
+    /// Note that we don't check the return value from the C `dma_set_coherent_mask` as the DMA API
+    /// guarantees that the coherent DMA mask can be set to the same or smaller than the streaming
+    /// DMA mask.
+    fn dma_set_mask_and_coherent(&mut self, mask: u64) -> Result {
+        // SAFETY: By the type invariant of `device::Device`, `self.as_ref().as_raw()` is valid.
+        let ret = unsafe { bindings::dma_set_mask_and_coherent(self.as_ref().as_raw(), mask) };
+        if ret != 0 {
+            Err(Error::from_errno(ret))
+        } else {
+            Ok(())
+        }
+    }
+
+    /// Same as [`Self::dma_set_mask_and_coherent`], but set the mask only for streaming mappings.
+    fn dma_set_mask(&mut self, mask: u64) -> Result {
+        // SAFETY: By the type invariant of `device::Device`, `self.as_ref().as_raw()` is valid.
+        let ret = unsafe { bindings::dma_set_mask(self.as_ref().as_raw(), mask) };
+        if ret != 0 {
+            Err(Error::from_errno(ret))
+        } else {
+            Ok(())
+        }
+    }
+}
 
 /// Possible attributes associated with a DMA mapping.
 ///
@@ -374,3 +402,15 @@ macro_rules! dma_write {
         }
     };
 }
+
+/// Helper function to set the bit mask for DMA addressing.
+pub const fn dma_bit_mask(n: usize) -> u64 {
+    if n > 64 {
+        return 0;
+    }
+    if n == 64 {
+        !0
+    } else {
+        (1 << (n)) - 1
+    }
+}
-- 
2.43.0