[RFC PATCH 7/8] rust: add firmware abstractions

[Danilo Krummrich]

Hi Luis and Russ,

I just noted I forgot to add you to this patch, sorry for that.

Please find the full series and previous discussions in [1].

- Danilo

[1] https://lore.kernel.org/rust-for-linux/20240520172059.181256-1-dakr@redhat.com/

On Mon, May 20, 2024 at 07:24:19PM +0200, Danilo Krummrich wrote:
> Add an abstraction around the kernels firmware API to request firmware
> images. The abstraction provides functions to access the firmware
> buffer and / or copy it to a new buffer allocated with a given allocator
> backend.
> 
> The firmware is released once the abstraction is dropped.
> 
> Signed-off-by: Danilo Krummrich <dakr at redhat.com>
> ---
>  rust/bindings/bindings_helper.h |  1 +
>  rust/kernel/firmware.rs         | 74 +++++++++++++++++++++++++++++++++
>  rust/kernel/lib.rs              |  1 +
>  3 files changed, 76 insertions(+)
>  create mode 100644 rust/kernel/firmware.rs
> 
> diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
> index b245db8d5a87..e4ffc47da5ec 100644
> --- a/rust/bindings/bindings_helper.h
> +++ b/rust/bindings/bindings_helper.h
> @@ -14,6 +14,7 @@
>  #include <kunit/test.h>
>  #include <linux/errname.h>
>  #include <linux/ethtool.h>
> +#include <linux/firmware.h>
>  #include <linux/jiffies.h>
>  #include <linux/mdio.h>
>  #include <linux/pci.h>
> diff --git a/rust/kernel/firmware.rs b/rust/kernel/firmware.rs
> new file mode 100644
> index 000000000000..700504fb3c9c
> --- /dev/null
> +++ b/rust/kernel/firmware.rs
> @@ -0,0 +1,74 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +//! Firmware abstraction
> +//!
> +//! C header: [`include/linux/firmware.h`](../../../../include/linux/firmware.h")
> +
> +use crate::{bindings, device::Device, error::Error, error::Result, str::CStr, types::Opaque};
> +
> +/// Abstraction around a C firmware struct.
> +///
> +/// This is a simple abstraction around the C firmware API. Just like with the C API, firmware can
> +/// be requested. Once requested the abstraction provides direct access to the firmware buffer as
> +/// `&[u8]`. Alternatively, the firmware can be copied to a new buffer using `Firmware::copy`. The
> +/// firmware is released once [`Firmware`] is dropped.
> +///
> +/// # Examples
> +///
> +/// ```
> +/// let fw = Firmware::request("path/to/firmware.bin", dev.as_ref())?;
> +/// driver_load_firmware(fw.data());
> +/// ```
> +pub struct Firmware(Opaque<*const bindings::firmware>);
> +
> +impl Firmware {
> +    /// Send a firmware request and wait for it. See also `bindings::request_firmware`.
> +    pub fn request(name: &CStr, dev: &Device) -> Result<Self> {
> +        let fw = Opaque::uninit();
> +
> +        let ret = unsafe { bindings::request_firmware(fw.get(), name.as_char_ptr(), dev.as_raw()) };
> +        if ret != 0 {
> +            return Err(Error::from_errno(ret));
> +        }
> +
> +        Ok(Firmware(fw))
> +    }
> +
> +    /// Send a request for an optional fw module. See also `bindings::request_firmware_nowarn`.
> +    pub fn request_nowarn(name: &CStr, dev: &Device) -> Result<Self> {
> +        let fw = Opaque::uninit();
> +
> +        let ret = unsafe {
> +            bindings::firmware_request_nowarn(fw.get(), name.as_char_ptr(), dev.as_raw())
> +        };
> +        if ret != 0 {
> +            return Err(Error::from_errno(ret));
> +        }
> +
> +        Ok(Firmware(fw))
> +    }
> +
> +    /// Returns the size of the requested firmware in bytes.
> +    pub fn size(&self) -> usize {
> +        unsafe { (*(*self.0.get())).size }
> +    }
> +
> +    /// Returns the requested firmware as `&[u8]`.
> +    pub fn data(&self) -> &[u8] {
> +        unsafe { core::slice::from_raw_parts((*(*self.0.get())).data, self.size()) }
> +    }
> +}
> +
> +impl Drop for Firmware {
> +    fn drop(&mut self) {
> +        unsafe { bindings::release_firmware(*self.0.get()) };
> +    }
> +}
> +
> +// SAFETY: `Firmware` only holds a pointer to a C firmware struct, which is safe to be used from any
> +// thread.
> +unsafe impl Send for Firmware {}
> +
> +// SAFETY: `Firmware` only holds a pointer to a C firmware struct, references to which are safe to
> +// be used from any thread.
> +unsafe impl Sync for Firmware {}
> diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
> index 6415968ee3b8..ed97d131661a 100644
> --- a/rust/kernel/lib.rs
> +++ b/rust/kernel/lib.rs
> @@ -35,6 +35,7 @@
>  #[cfg(CONFIG_DRM = "y")]
>  pub mod drm;
>  pub mod error;
> +pub mod firmware;
>  pub mod init;
>  pub mod ioctl;
>  #[cfg(CONFIG_KUNIT)]
> -- 
> 2.45.1
>