linux-kernel - Re: [PATCH v2 2/2] rust: add firmware abstractions

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Date: Tue, 11 Jun 2024 08:31:46 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: Danilo Krummrich <dakr@...hat.com>
Cc: rafael@...nel.org, mcgrof@...nel.org, russell.h.weight@...el.com,
	ojeda@...nel.org, alex.gaynor@...il.com, wedsonaf@...il.com,
	boqun.feng@...il.com, gary@...yguo.net, bjorn3_gh@...tonmail.com,
	benno.lossin@...ton.me, a.hindborg@...sung.com,
	aliceryhl@...gle.com, airlied@...il.com, fujita.tomonori@...il.com,
	pstanner@...hat.com, ajanulgu@...hat.com, lyude@...hat.com,
	rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] rust: add firmware abstractions

On Mon, Jun 10, 2024 at 08:02:28PM +0200, Danilo Krummrich wrote:
> Add an abstraction around the kernels firmware API to request firmware
> images. The abstraction provides functions to access the firmware's size
> and backing buffer.
> 
> The firmware is released once the abstraction instance is dropped.
> 
> Signed-off-by: Danilo Krummrich <dakr@...hat.com>
> ---
>  rust/bindings/bindings_helper.h |   1 +
>  rust/kernel/firmware.rs         | 107 ++++++++++++++++++++++++++++++++
>  rust/kernel/lib.rs              |   1 +
>  3 files changed, 109 insertions(+)
>  create mode 100644 rust/kernel/firmware.rs
> 
> diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
> index ddb5644d4fd9..18a3f05115cb 100644
> --- a/rust/bindings/bindings_helper.h
> +++ b/rust/bindings/bindings_helper.h
> @@ -9,6 +9,7 @@
>  #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/phy.h>
> diff --git a/rust/kernel/firmware.rs b/rust/kernel/firmware.rs
> new file mode 100644
> index 000000000000..7ff4c325f670
> --- /dev/null
> +++ b/rust/kernel/firmware.rs
> @@ -0,0 +1,107 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +//! Firmware abstraction
> +//!
> +//! C header: [`include/linux/firmware.h`](srctree/include/linux/firmware.h")
> +
> +use crate::{bindings, device::Device, error::Error, error::Result, str::CStr};
> +use core::ptr::NonNull;
> +
> +// One of the following: `bindings::request_firmware`, `bindings::firmware_request_nowarn`,
> +// `firmware_request_platform`, `bindings::request_firmware_direct`
> +type FwFunc =
> +    unsafe extern "C" fn(*mut *const bindings::firmware, *const i8, *mut bindings::device) -> i32;
> +
> +/// Abstraction around a C `struct firmware`.
> +///
> +/// 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]`. The firmware is released once [`Firmware`] is dropped.
> +///
> +/// # Invariants
> +///
> +/// The pointer is valid, and has ownership over the instance of `struct firmware`.
> +///
> +/// # Examples
> +///
> +/// ```
> +/// use kernel::firmware::Firmware;
> +///
> +/// let fw = Firmware::request("path/to/firmware.bin", dev.as_ref())?;
> +/// driver_load_firmware(fw.data());
> +/// ```
> +pub struct Firmware(NonNull<bindings::firmware>);
> +
> +impl Firmware {
> +    fn request_internal(name: &CStr, dev: &Device, func: FwFunc) -> Result<Self> {
> +        let mut fw: *mut bindings::firmware = core::ptr::null_mut();
> +        let pfw: *mut *mut bindings::firmware = &mut fw;
> +
> +        // SAFETY: `pfw` is a valid pointer to a NULL initialized `bindings::firmware` pointer.
> +        // `name` and `dev` are valid as by their type invariants.
> +        let ret = unsafe { func(pfw as _, name.as_char_ptr(), dev.as_raw()) };
> +        if ret != 0 {
> +            return Err(Error::from_errno(ret));
> +        }
> +
> +        // SAFETY: `func` not bailing out with a non-zero error code, guarantees that `fw` is a
> +        // valid pointer to `bindings::firmware`.
> +        Ok(Firmware(unsafe { NonNull::new_unchecked(fw) }))
> +    }
> +
> +    /// Send a firmware request and wait for it. See also `bindings::request_firmware`.
> +    pub fn request(name: &CStr, dev: &Device) -> Result<Self> {
> +        Self::request_internal(name, dev, bindings::request_firmware)
> +    }

How does this handle when CONFIG_FW_LOADER is not enabled?  Why are you
building these bindings if that option is not checked?

> +
> +    /// Send a request for an optional firmware module. See also
> +    /// `bindings::firmware_request_nowarn`.
> +    pub fn request_nowarn(name: &CStr, dev: &Device) -> Result<Self> {
> +        Self::request_internal(name, dev, bindings::firmware_request_nowarn)
> +    }
> +
> +    /// Send a request for a firmware with platform-fw fallback. See also
> +    /// `bindings::firmware_request_platform`.
> +    pub fn request_platform(name: &CStr, dev: &Device) -> Result<Self> {
> +        Self::request_internal(name, dev, bindings::firmware_request_platform)
> +    }
> +
> +    /// Send a request for a firmware directly without usermode helper. See also
> +    /// `bindings::request_firmware_direct`.
> +    pub fn request_direct(name: &CStr, dev: &Device) -> Result<Self> {
> +        Self::request_internal(name, dev, bindings::request_firmware_direct)
> +    }

Why just these variants?  Why not just add the ones that people actually
need instead of a random assortment like you choose here :)

thanks,

greg k-h