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

[Zhi Wang <zhiw@nvidia.com>]

On Mon, 20 May 2024 19:24:19 +0200
Danilo Krummrich <dakr@redhat.com> 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.
> 

Was playing with firmware extractions based on this patch.
Unfortunately I ended up with a lot of pointer operations, unsafe
statements.

As we know many vendors have a C headers for the definitions of the
firwmare content, the driver extract the data by applying a struct
pointer on it.

But in rust, I feel it would nice that we can also have a common
firmware extractor for drivers, that can wrap the pointer operations,
take a list of the firmware struct members that converted from C headers
as the input, offer the driver some common ABI methods to query them.
Maybe that would ease the pain a lot.

Thanks,
Zhi.

> The firmware is released once the abstraction is dropped.
> 
> Signed-off-by: Danilo Krummrich <dakr@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)]