samples: rust: add Rust PCI sample driver

This commit adds a sample Rust PCI driver for QEMU's "pci-testdev"
device. To enable this device QEMU has to be called with
`-device pci-testdev`.

The same driver shows how to use the PCI device / driver abstractions,
as well as how to request and map PCI BARs, including a short sequence of
MMIO operations.

Signed-off-by: Danilo Krummrich <dakr@kernel.org>

MAINTAINERS

@@ -17940,6 +17940,7 @@ F:	include/linux/of_pci.h
 F:	include/linux/pci*
 F:	include/uapi/linux/pci*
 F:	rust/kernel/pci.rs
+F:	samples/rust/rust_driver_pci.rs
 
 PCIE DRIVER FOR AMAZON ANNAPURNA LABS
 M:	Jonathan Chocron <jonnyc@amazon.com>

samples/rust/Kconfig

@@ -30,6 +30,17 @@ config SAMPLE_RUST_PRINT
 
 	  If unsure, say N.
 
+config SAMPLE_RUST_DRIVER_PCI
+	tristate "PCI Driver"
+	depends on PCI
+	help
+	  This option builds the Rust PCI driver sample.
+
+	  To compile this as a module, choose M here:
+	  the module will be called driver_pci.
+
+	  If unsure, say N.
+
 config SAMPLE_RUST_HOSTPROGS
 	bool "Host programs"
 	help

samples/rust/Makefile

@@ -2,5 +2,6 @@
 
 obj-$(CONFIG_SAMPLE_RUST_MINIMAL)		+= rust_minimal.o
 obj-$(CONFIG_SAMPLE_RUST_PRINT)			+= rust_print.o
+obj-$(CONFIG_SAMPLE_RUST_DRIVER_PCI)		+= rust_driver_pci.o
 
 subdir-$(CONFIG_SAMPLE_RUST_HOSTPROGS)		+= hostprogs

samples/rust/rust_driver_pci.rs

@@ -0,0 +1,109 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Rust PCI driver sample (based on QEMU's `pci-testdev`).
+//!
+//! To make this driver probe, QEMU must be run with `-device pci-testdev`.
+
+use kernel::{bindings, c_str, devres::Devres, pci, prelude::*};
+
+struct Regs;
+
+impl Regs {
+    const TEST: usize = 0x0;
+    const OFFSET: usize = 0x4;
+    const DATA: usize = 0x8;
+    const COUNT: usize = 0xC;
+    const END: usize = 0x10;
+}
+
+type Bar0 = pci::Bar<{ Regs::END }>;
+
+#[derive(Debug)]
+struct TestIndex(u8);
+
+impl TestIndex {
+    const NO_EVENTFD: Self = Self(0);
+}
+
+struct SampleDriver {
+    pdev: pci::Device,
+    bar: Devres<Bar0>,
+}
+
+kernel::pci_device_table!(
+    PCI_TABLE,
+    MODULE_PCI_TABLE,
+    <SampleDriver as pci::Driver>::IdInfo,
+    [(
+        pci::DeviceId::new(bindings::PCI_VENDOR_ID_REDHAT, 0x5),
+        TestIndex::NO_EVENTFD
+    )]
+);
+
+impl SampleDriver {
+    fn testdev(index: &TestIndex, bar: &Bar0) -> Result<u32> {
+        // Select the test.
+        bar.writeb(index.0, Regs::TEST);
+
+        let offset = u32::from_le(bar.readl(Regs::OFFSET)) as usize;
+        let data = bar.readb(Regs::DATA);
+
+        // Write `data` to `offset` to increase `count` by one.
+        //
+        // Note that we need `try_writeb`, since `offset` can't be checked at compile-time.
+        bar.try_writeb(data, offset)?;
+
+        Ok(u32::from_le(bar.readl(Regs::COUNT)))
+    }
+}
+
+impl pci::Driver for SampleDriver {
+    type IdInfo = TestIndex;
+
+    const ID_TABLE: pci::IdTable<Self::IdInfo> = &PCI_TABLE;
+
+    fn probe(
+        pdev: &mut pci::Device,
+        _id: &pci::DeviceId,
+        info: &Self::IdInfo,
+    ) -> Result<Pin<KBox<Self>>> {
+        dev_dbg!(pdev.as_ref(), "Probe Rust PCI driver sample.\n");
+
+        pdev.enable_device_mem()?;
+        pdev.set_master();
+
+        let bar = pdev.iomap_region_sized::<{ Regs::END }>(0, c_str!("rust_driver_pci"))?;
+
+        let drvdata = KBox::new(
+            Self {
+                pdev: pdev.clone(),
+                bar,
+            },
+            GFP_KERNEL,
+        )?;
+
+        let bar = drvdata.bar.try_access().ok_or(ENXIO)?;
+
+        dev_info!(
+            pdev.as_ref(),
+            "pci-testdev data-match count: {}\n",
+            Self::testdev(info, &bar)?
+        );
+
+        Ok(drvdata.into())
+    }
+}
+
+impl Drop for SampleDriver {
+    fn drop(&mut self) {
+        dev_dbg!(self.pdev.as_ref(), "Remove Rust PCI driver sample.\n");
+    }
+}
+
+kernel::module_pci_driver! {
+    type: SampleDriver,
+    name: "rust_driver_pci",
+    author: "Danilo Krummrich",
+    description: "Rust PCI driver",
+    license: "GPL v2",
+}