Re: [PATCH 7/7] rust: samples: add the v4l2 sample driver

[Elle Rhumsaa <elle@weathered-steel.dev>]

On Mon, Aug 18, 2025 at 02:49:53AM -0300, Daniel Almeida wrote:
> This driver is the only user of the v4l2 abstractions at the moment. It
> serves as a means to validate the abstractions by proving that the
> device is actually registered as /dev/videoX, and it can be opened and
> queried by v4l2-ctl, while also serving as a display of the current v4l2
> support in Rust, as well as a blueprint for more elaborate Rust v4l2
> drivers in the future.
> 
> Signed-off-by: Daniel Almeida <daniel.almeida@collabora.com>
> ---
>  MAINTAINERS                      |   1 +
>  samples/rust/Kconfig             |  11 +++
>  samples/rust/Makefile            |   1 +
>  samples/rust/rust_driver_v4l2.rs | 145 +++++++++++++++++++++++++++++++++++++++
>  4 files changed, 158 insertions(+)
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 6fc5d57950e474d73d5d65271a0394efc5a8960b..14521bc0585503992da582f2cee361666985e39f 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -15440,6 +15440,7 @@ L:	linux-media@vger.kernel.org
>  L:	rust-for-linux@vger.kernel.org
>  S:	Supported
>  F:	rust/media
> +F:	sample/rust/rust_driver_v4l2.rs
>  
>  MEDIATEK BLUETOOTH DRIVER
>  M:	Sean Wang <sean.wang@mediatek.com>
> diff --git a/samples/rust/Kconfig b/samples/rust/Kconfig
> index 7f7371a004ee0a8f67dca99c836596709a70c4fa..64422acf1e9da9d05f904e14fd423b3b4aef173a 100644
> --- a/samples/rust/Kconfig
> +++ b/samples/rust/Kconfig
> @@ -105,6 +105,17 @@ config SAMPLE_RUST_DRIVER_AUXILIARY
>  
>  	  If unsure, say N.
>  
> +config SAMPLE_RUST_DRIVER_V4L2
> +	tristate "Video4Linux2 driver"
> +	depends on MEDIA_SUPPORT && VIDEO_DEV
> +	help
> +	  This option builds the Rust V4L2 driver sample.
> +
> +	  To compile this as a module, choose M here:
> +	  the module will be called rust_driver_v4l2.
> +
> +	  If unsure, say N.
> +
>  config SAMPLE_RUST_HOSTPROGS
>  	bool "Host programs"
>  	help
> diff --git a/samples/rust/Makefile b/samples/rust/Makefile
> index bd2faad63b4f3befe7d1ed5139fe25c7a8b6d7f6..57e21f0373938bb70b4cb400ea550010895b4c94 100644
> --- a/samples/rust/Makefile
> +++ b/samples/rust/Makefile
> @@ -9,6 +9,7 @@ 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_AUXILIARY)	+= rust_driver_auxiliary.o
> +obj-$(CONFIG_SAMPLE_RUST_DRIVER_V4L2)		+= rust_driver_v4l2.o
>  obj-$(CONFIG_SAMPLE_RUST_CONFIGFS)		+= rust_configfs.o
>  
>  rust_print-y := rust_print_main.o rust_print_events.o
> diff --git a/samples/rust/rust_driver_v4l2.rs b/samples/rust/rust_driver_v4l2.rs
> new file mode 100644
> index 0000000000000000000000000000000000000000..a3ef98a613f2fed9e8589f0761ce7e43029c02b6
> --- /dev/null
> +++ b/samples/rust/rust_driver_v4l2.rs
> @@ -0,0 +1,145 @@
> +// SPDX-License-Identifier: GPL-2.0
> +// SPDX-copyrightText: Copyright (C) 2025 Collabora Ltd.
> +
> +//! Rust V4L2 sample driver.
> +//!
> +//! This sample demonstrates how to:
> +//! - Register a V4L2 device (struct v4l2_device),
> +//! - Register a video node (struct video_device) using the Rust V4L2
> +//!   abstractions,
> +//! - Implement support for a V4L2 ioctl in a driver.
> +//!
> +//! It implements only `VIDIOC_QUERYCAP` and minimal open/close handling.
> +
> +use kernel::{
> +    c_str,
> +    device::Core,
> +    media::v4l2::{
> +        self,
> +        caps::{self, DeviceCaps},
> +        video,
> +    },
> +    of, platform,
> +    prelude::*,
> +    types::ARef,
> +    ThisModule,
> +};
> +
> +/// The private data associated with the V4L2 device.
> +#[pin_data]
> +struct Data {}
> +
> +/// The private data associated with a V4L2 device node, i.e. `struct
> +/// video_device`.
> +#[pin_data]
> +struct VideoData {}
> +
> +/// The private data associated with a V4L2 file, i.e. `struct v4l2_fh`.
> +#[pin_data]
> +struct File {}
> +
> +impl v4l2::file::DriverFile for File {
> +    type Driver = SampleDriver;
> +
> +    const MODULE: &'static ThisModule = &THIS_MODULE;
> +
> +    fn open(_vdev: &v4l2::video::Device<Self::Driver>) -> impl PinInit<Self, Error> {
> +        try_pin_init!(Self {})
> +    }
> +}
> +
> +struct SampleDriver {
> +    _pdev: ARef<platform::Device>,
> +    _v4l2_reg: v4l2::device::Registration<Self>,
> +    video_reg: video::Registration<Self>,
> +}
> +
> +impl v4l2::device::Driver for SampleDriver {
> +    type Data = Data;
> +}
> +
> +#[vtable]
> +impl video::Driver for SampleDriver {
> +    type Data = VideoData;
> +    type File = File;
> +
> +    const NODE_TYPE: video::NodeType = video::NodeType::Video;
> +    const DIRECTION: video::Direction = video::Direction::Rx;
> +    const NAME: &'static CStr = c_str!("rv4l2");
> +    const CAPS: DeviceCaps = caps::device_caps::VIDEO_CAPTURE;
> +
> +    fn querycap(
> +        _file: &v4l2::file::File<Self::File>,
> +        _data: &<Self as video::Driver>::Data,
> +        cap: &mut caps::Capabilities,
> +    ) -> Result {
> +        cap.set_driver(c_str!("rv4l2"))?;
> +        cap.set_card(c_str!("rv4l2"))?;
> +        cap.set_bus_info(c_str!("platform:rv4l2"))?;
> +
> +        cap.set_device_caps(Self::CAPS);
> +        Ok(())
> +    }
> +}
> +
> +kernel::of_device_table!(
> +    OF_TABLE,
> +    MODULE_OF_TABLE,
> +    <SampleDriver as platform::Driver>::IdInfo,
> +    [(of::DeviceId::new(c_str!("test, rust-v4l2")), ())]
> +);
> +
> +impl platform::Driver for SampleDriver {
> +    type IdInfo = ();
> +    const OF_ID_TABLE: Option<of::IdTable<Self::IdInfo>> = Some(&OF_TABLE);
> +
> +    fn probe(
> +        pdev: &platform::Device<Core>,
> +        _info: Option<&Self::IdInfo>,
> +    ) -> Result<Pin<KBox<Self>>> {
> +        let dev = pdev.as_ref();
> +
> +        let v4l2_reg =
> +            v4l2::device::Registration::<Self>::new(dev, try_pin_init!(Data {}), GFP_KERNEL)?;
> +
> +        let video_reg = video::Registration::<Self>::new(
> +            v4l2_reg.device(),
> +            try_pin_init!(VideoData {}),
> +            GFP_KERNEL,
> +        )?;
> +
> +        let this = KBox::new(
> +            Self {
> +                _pdev: pdev.into(),
> +                _v4l2_reg: v4l2_reg,
> +                video_reg,
> +            },
> +            GFP_KERNEL,
> +        )?;
> +
> +        dev_info!(
> +            dev,
> +            "Registered /dev/video{}\n",
> +            this.video_reg.device().num()
> +        );
> +        Ok(this.into())
> +    }
> +
> +    fn unbind(pdev: &platform::Device<Core>, _this: Pin<&Self>) {
> +        dev_info!(pdev.as_ref(), "Unbinding Rust V4L2 sample driver\n");
> +    }
> +}
> +
> +impl Drop for SampleDriver {
> +    fn drop(&mut self) {
> +        dev_dbg!(self._pdev.as_ref(), "Rust V4L2 sample driver removed\n");
> +    }
> +}
> +
> +kernel::module_platform_driver! {
> +    type: SampleDriver,
> +    name: "rust_driver_v4l2",
> +    authors: ["Daniel Almeida"],
> +    description: "Rust V4L2 sample video driver",
> +    license: "GPL v2",
> +}
> 
> -- 
> 2.50.1

Reviewed-by: Elle Rhumsaa <elle@weathered-steel.dev>