[PATCH v13 5/7] samples: rust: add Rust dma test sample driver

[Abdiel Janulgue <abdiel.janulgue@gmail.com>]

Add a simple driver to excercise the basics of the Rust DMA
coherent allocator bindings.

Suggested-by: Danilo Krummrich <dakr@kernel.org>
Signed-off-by: Abdiel Janulgue <abdiel.janulgue@gmail.com>
---
 samples/rust/Kconfig     |  11 +++++
 samples/rust/Makefile    |   1 +
 samples/rust/rust_dma.rs | 104 +++++++++++++++++++++++++++++++++++++++
 3 files changed, 116 insertions(+)
 create mode 100644 samples/rust/rust_dma.rs

diff --git a/samples/rust/Kconfig b/samples/rust/Kconfig
index 3b6eae84b297..04bbba870bd1 100644
--- a/samples/rust/Kconfig
+++ b/samples/rust/Kconfig
@@ -78,4 +78,15 @@ config SAMPLE_RUST_HOSTPROGS
 
 	  If unsure, say N.
 
+config SAMPLE_RUST_DRIVER_DMA
+	tristate "DMA test driver"
+	depends on PCI
+	help
+	  This option builds the Rust dma test driver sample.
+
+	  To compile this as a module, choose M here:
+	  the module will be called dma.
+
+	  If unsure, say N.
+
 endif # SAMPLES_RUST
diff --git a/samples/rust/Makefile b/samples/rust/Makefile
index 0dbc6d90f1ef..1a9aff6e8d6a 100644
--- a/samples/rust/Makefile
+++ b/samples/rust/Makefile
@@ -7,6 +7,7 @@ obj-$(CONFIG_SAMPLE_RUST_PRINT)			+= rust_print.o
 obj-$(CONFIG_SAMPLE_RUST_DRIVER_PCI)		+= rust_driver_pci.o
 obj-$(CONFIG_SAMPLE_RUST_DRIVER_PLATFORM)	+= rust_driver_platform.o
 obj-$(CONFIG_SAMPLE_RUST_DRIVER_FAUX)		+= rust_driver_faux.o
+obj-$(CONFIG_SAMPLE_RUST_DRIVER_DMA)		+= rust_dma.o
 
 rust_print-y := rust_print_main.o rust_print_events.o
 
diff --git a/samples/rust/rust_dma.rs b/samples/rust/rust_dma.rs
new file mode 100644
index 000000000000..aed55ae4dcfe
--- /dev/null
+++ b/samples/rust/rust_dma.rs
@@ -0,0 +1,104 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Rust DMA api test (based on QEMU's `pci-testdev`).
+//!
+//! To make this driver probe, QEMU must be run with `-device pci-testdev`.
+
+use kernel::{bindings, dma::CoherentAllocation, pci, prelude::*};
+
+struct DmaSampleDriver {
+    pdev: pci::Device,
+    ca: kernel::devres::Devres<CoherentAllocation<MyStruct>>,
+}
+
+const TEST_VALUES: [(u32, u32); 5] = [
+    (0xa, 0xb),
+    (0xc, 0xd),
+    (0xe, 0xf),
+    (0xab, 0xba),
+    (0xcd, 0xef),
+];
+
+struct MyStruct {
+    h: u32,
+    b: u32,
+}
+
+impl MyStruct {
+    fn new(h: u32, b: u32) -> Self {
+        Self { h, b }
+    }
+}
+// SAFETY: All bit patterns are acceptable values for `MyStruct`.
+unsafe impl kernel::transmute::AsBytes for MyStruct {}
+// SAFETY: Instances of `MyStruct` have no uninitialized portions.
+unsafe impl kernel::transmute::FromBytes for MyStruct {}
+
+kernel::pci_device_table!(
+    PCI_TABLE,
+    MODULE_PCI_TABLE,
+    <DmaSampleDriver as pci::Driver>::IdInfo,
+    [(
+        pci::DeviceId::from_id(bindings::PCI_VENDOR_ID_REDHAT, 0x5),
+        ()
+    )]
+);
+
+impl pci::Driver for DmaSampleDriver {
+    type IdInfo = ();
+    const ID_TABLE: pci::IdTable<Self::IdInfo> = &PCI_TABLE;
+
+    fn probe(pdev: &mut pci::Device, _info: &Self::IdInfo) -> Result<Pin<KBox<Self>>> {
+        let dev = pdev.as_mut();
+
+        dev.dma_set_mask_and_coherent(kernel::dma::dma_bit_mask(64))?;
+
+        dev_info!(dev, "Probe DMA test driver.\n");
+
+        let ca: kernel::devres::Devres<CoherentAllocation<MyStruct>> =
+            CoherentAllocation::alloc_coherent(dev, TEST_VALUES.len(), GFP_KERNEL)?;
+
+        || -> Result {
+            let reg = ca.try_access().ok_or(ENXIO)?;
+
+            for (i, value) in TEST_VALUES.into_iter().enumerate() {
+                kernel::dma_write!(reg[i] = MyStruct::new(value.0, value.1));
+            }
+
+            Ok(())
+        }()?;
+
+        let drvdata = KBox::new(
+            Self {
+                pdev: pdev.clone(),
+                ca,
+            },
+            GFP_KERNEL,
+        )?;
+
+        Ok(drvdata.into())
+    }
+}
+
+impl Drop for DmaSampleDriver {
+    fn drop(&mut self) {
+        dev_info!(self.pdev.as_ref(), "Unload DMA test driver.\n");
+
+        let _ = || -> Result {
+            let reg = self.ca.try_access().ok_or(ENXIO)?;
+            for (i, value) in TEST_VALUES.into_iter().enumerate() {
+                assert_eq!(kernel::dma_read!(reg[i].h), value.0);
+                assert_eq!(kernel::dma_read!(reg[i].b), value.1);
+            }
+            Ok(())
+        }();
+    }
+}
+
+kernel::module_pci_driver! {
+    type: DmaSampleDriver,
+    name: "rust_dma",
+    author: "Abdiel Janulgue",
+    description: "Rust DMA test",
+    license: "GPL v2",
+}
-- 
2.43.0