Re: [PATCH v3 13/16] samples: rust: add Rust PCI sample driver

[Rob Herring <robh@kernel.org>]

On Tue, Oct 22, 2024 at 11:31:50PM +0200, Danilo Krummrich wrote:
> 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`.

Note that the DT unittests also use this device. So this means we have 2 
drivers that bind to the device. Probably it's okay, but does make 
them somewhat mutually-exclusive.
 
> 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                     |   1 +
>  samples/rust/Kconfig            |  11 ++++
>  samples/rust/Makefile           |   1 +
>  samples/rust/rust_driver_pci.rs | 109 ++++++++++++++++++++++++++++++++
>  4 files changed, 122 insertions(+)
>  create mode 100644 samples/rust/rust_driver_pci.rs
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 2d00d3845b4a..d9c512a3e72b 100644
> --- a/MAINTAINERS
> +++ b/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>
> diff --git a/samples/rust/Kconfig b/samples/rust/Kconfig
> index b0f74a81c8f9..6d468193cdd8 100644
> --- a/samples/rust/Kconfig
> +++ b/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
> diff --git a/samples/rust/Makefile b/samples/rust/Makefile
> index 03086dabbea4..b66767f4a62a 100644
> --- a/samples/rust/Makefile
> +++ b/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
> diff --git a/samples/rust/rust_driver_pci.rs b/samples/rust/rust_driver_pci.rs
> new file mode 100644
> index 000000000000..d24dc1fde9e8
> --- /dev/null
> +++ b/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;

The C version of readl takes care of from_le for you. Why not here?

Also, can't we do better with rust and make this a generic:

let offset = bar.read::<u32>(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)))
> +    }
> +}