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

[Danilo Krummrich]

On Tue, May 21, 2024 at 08:32:31AM +0300, Zhi Wang wrote:
> On Mon, 20 May 2024 19:24:19 +0200
> Danilo Krummrich <dakr at 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.

So, you mean some abstraction that takes a list of types, offsets in the
firmware and a reference to the firmware itself and provides references to the
corresponding objects?

I agree it might be helpful to have some common infrastructure for this, but the
operations on it would still be unsafe, since ultimately it involves
dereferencing pointers.

> 
> Thanks,
> Zhi.
> 
> > 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)]
>