linux/rust/kernel/firmware.rs

// 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::to_result,
    ffi,
    prelude::*,
    str::{CStr, CStrExt as _},
};
use core::ptr::NonNull;

/// # Invariants
///
/// One of the following: `bindings::request_firmware`, `bindings::firmware_request_nowarn`,
/// `bindings::firmware_request_platform`, `bindings::request_firmware_direct`.
struct FwFunc(
    unsafe extern "C" fn(
        *mut *const bindings::firmware,
        *const ffi::c_char,
        *mut bindings::device,
    ) -> i32,
);

impl FwFunc {
    fn request() -> Self {
        Self(bindings::request_firmware)
    }

    fn request_nowarn() -> Self {
        Self(bindings::firmware_request_nowarn)
    }
}

/// 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`.
///
/// The `Firmware`'s backing buffer is not modified.
///
/// # Examples
///
/// ```no_run
/// # use kernel::{device::Device, firmware::Firmware, sync::aref::ARef};
/// # fn no_run(dev: ARef<Device>) -> Result<(), Error> {
/// let fw = Firmware::request(c"path/to/firmware.bin", &dev)?;
/// let blob = fw.data();
///
/// # Ok(())
/// # }
/// ```
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;
        let pfw: *mut *const bindings::firmware = pfw.cast();

        // 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.0(pfw, 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, FwFunc::request())
    }

    /// 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, FwFunc::request_nowarn())
    }

    fn as_raw(&self) -> *mut bindings::firmware {
        self.0.as_ptr()
    }

    /// Returns the size of the requested firmware in bytes.
    pub fn size(&self) -> usize {
        // SAFETY: `self.as_raw()` is valid by the type invariant.
        unsafe { (*self.as_raw()).size }
    }

    /// Returns the requested firmware as `&[u8]`.
    pub fn data(&self) -> &[u8] {
        // SAFETY: `self.as_raw()` is valid by the type invariant. Additionally,
        // `bindings::firmware` guarantees, if successfully requested, that
        // `bindings::firmware::data` has a size of `bindings::firmware::size` bytes.
        unsafe { core::slice::from_raw_parts((*self.as_raw()).data, self.size()) }
    }
}

impl Drop for Firmware {
    fn drop(&mut self) {
        // SAFETY: `self.as_raw()` is valid by the type invariant.
        unsafe { bindings::release_firmware(self.as_raw()) };
    }
}

/// Load firmware directly into the caller-provided `buf`.
///
/// On success the firmware image has been copied into `buf`; the caller accesses the data
/// through `buf` itself.
///
/// This is intentionally a stand-alone function rather than a `Firmware` constructor. For
/// the `into_buf` path, the firmware data lives in the caller's `buf`, not in a
/// kernel-owned buffer, so returning a `Firmware` would expose `Firmware::data()` as a
/// second handle aliasing `buf` (and `release_firmware()` does not free `buf` anyway).
pub fn request_into_buf(name: &CStr, dev: &Device, buf: &mut [u8]) -> Result {
    // `as_mut_ptr()` on an empty slice returns a non-NULL pointer to
    // memory which the loader does not own. Passing that pointer with `size == 0`
    // makes the loader believe that it is buffer it allocated itself, so when
    // `release_firmware()` is called, it will vfree the pointer and trigger a
    // bug. Reject empty slices to avoid this situation.
    if buf.is_empty() {
        return Err(EINVAL);
    }

    let mut fw: *const bindings::firmware = core::ptr::null();

    // SAFETY: `&raw mut fw` is a valid pointer to a NULL initialized `bindings::firmware` pointer.
    // `name` and `dev` are valid as by their type invariants. `buf` is a valid writable
    // buffer of `buf.len()` bytes.
    to_result(unsafe {
        bindings::request_firmware_into_buf(
            &raw mut fw,
            name.as_char_ptr(),
            dev.as_raw(),
            buf.as_mut_ptr().cast(),
            buf.len(),
        )
    })?;

    // The firmware bytes are now in `buf`, which the caller owns, so we don't need
    // the kernel to hang on to it any more.
    // SAFETY: `fw` is a valid pointer returned by `request_firmware_into_buf`.
    unsafe { bindings::release_firmware(fw) };

    Ok(())
}

// SAFETY: `Firmware` only holds a pointer to a C `struct firmware`, which is safe to be used from
// any thread.
unsafe impl Send for Firmware {}

// SAFETY: `Firmware` only holds a pointer to a C `struct firmware`, references to which are safe to
// be used from any thread.
unsafe impl Sync for Firmware {}

/// Create firmware .modinfo entries.
///
/// This macro is the counterpart of the C macro `MODULE_FIRMWARE()`, but instead of taking a
/// simple string literals, which is already covered by the `firmware` field of
/// [`crate::prelude::module!`], it allows the caller to pass a builder type, based on the
/// [`ModInfoBuilder`], which can create the firmware modinfo strings in a more flexible way.
///
/// Drivers should extend the [`ModInfoBuilder`] with their own driver specific builder type.
///
/// The `builder` argument must be a type which implements the following function.
///
/// `const fn create(module_name: &'static CStr) -> ModInfoBuilder`
///
/// `create` should pass the `module_name` to the [`ModInfoBuilder`] and, with the help of
/// it construct the corresponding firmware modinfo.
///
/// Typically, such contracts would be enforced by a trait, however traits do not (yet) support
/// const functions.
///
/// # Examples
///
/// ```
/// # mod module_firmware_test {
/// # use kernel::firmware;
/// # use kernel::prelude::*;
/// #
/// # struct MyModule;
/// #
/// # impl kernel::Module for MyModule {
/// #     fn init(_module: &'static ThisModule) -> Result<Self> {
/// #         Ok(Self)
/// #     }
/// # }
/// #
/// #
/// struct Builder<const N: usize>;
///
/// impl<const N: usize> Builder<N> {
///     const DIR: &'static str = "vendor/chip/";
///     const FILES: [&'static str; 3] = [ "foo", "bar", "baz" ];
///
///     const fn create(module_name: &'static kernel::str::CStr) -> firmware::ModInfoBuilder<N> {
///         let mut builder = firmware::ModInfoBuilder::new(module_name);
///
///         let mut i = 0;
///         while i < Self::FILES.len() {
///             builder = builder.new_entry()
///                 .push(Self::DIR)
///                 .push(Self::FILES[i])
///                 .push(".bin");
///
///                 i += 1;
///         }
///
///         builder
///      }
/// }
///
/// module! {
///    type: MyModule,
///    name: "module_firmware_test",
///    authors: ["Rust for Linux"],
///    description: "module_firmware! test module",
///    license: "GPL",
/// }
///
/// kernel::module_firmware!(Builder);
/// # }
/// ```
#[macro_export]
macro_rules! module_firmware {
    // The argument is the builder type without the const generic, since it's deferred from within
    // this macro. Hence, we can neither use `expr` nor `ty`.
    ($($builder:tt)*) => {
        const _: () = {
            const __MODULE_FIRMWARE_PREFIX: &'static $crate::str::CStr = if cfg!(MODULE) {
                c""
            } else {
                <LocalModule as $crate::ModuleMetadata>::NAME
            };

            #[link_section = ".modinfo"]
            #[used(compiler)]
            static __MODULE_FIRMWARE: [u8; $($builder)*::create(__MODULE_FIRMWARE_PREFIX)
                .build_length()] = $($builder)*::create(__MODULE_FIRMWARE_PREFIX).build();
        };
    };
}

/// Builder for firmware module info.
///
/// [`ModInfoBuilder`] is a helper component to flexibly compose firmware paths strings for the
/// .modinfo section in const context.
///
/// Therefore the [`ModInfoBuilder`] provides the methods [`ModInfoBuilder::new_entry`] and
/// [`ModInfoBuilder::push`], where the latter is used to push path components and the former to
/// mark the beginning of a new path string.
///
/// [`ModInfoBuilder`] is meant to be used in combination with [`kernel::module_firmware!`].
///
/// The const generic `N` as well as the `module_name` parameter of [`ModInfoBuilder::new`] is an
/// internal implementation detail and supplied through the above macro.
pub struct ModInfoBuilder<const N: usize> {
    buf: [u8; N],
    n: usize,
    module_name: &'static CStr,
}

impl<const N: usize> ModInfoBuilder<N> {
    /// Create an empty builder instance.
    pub const fn new(module_name: &'static CStr) -> Self {
        Self {
            buf: [0; N],
            n: 0,
            module_name,
        }
    }

    const fn push_internal(mut self, bytes: &[u8]) -> Self {
        let mut j = 0;

        if N == 0 {
            self.n += bytes.len();
            return self;
        }

        while j < bytes.len() {
            if self.n < N {
                self.buf[self.n] = bytes[j];
            }
            self.n += 1;
            j += 1;
        }
        self
    }

    /// Push an additional path component.
    ///
    /// Append path components to the [`ModInfoBuilder`] instance. Paths need to be separated
    /// with [`ModInfoBuilder::new_entry`].
    ///
    /// # Examples
    ///
    /// ```
    /// use kernel::firmware::ModInfoBuilder;
    ///
    /// # const DIR: &str = "vendor/chip/";
    /// # const fn no_run<const N: usize>(builder: ModInfoBuilder<N>) {
    /// let builder = builder.new_entry()
    ///     .push(DIR)
    ///     .push("foo.bin")
    ///     .new_entry()
    ///     .push(DIR)
    ///     .push("bar.bin");
    /// # }
    /// ```
    pub const fn push(self, s: &str) -> Self {
        // Check whether there has been an initial call to `next_entry()`.
        if N != 0 && self.n == 0 {
            crate::build_error!("Must call next_entry() before push().");
        }

        self.push_internal(s.as_bytes())
    }

    const fn push_module_name(self) -> Self {
        let mut this = self;
        let module_name = this.module_name;

        if !this.module_name.is_empty() {
            this = this.push_internal(module_name.to_bytes_with_nul());

            if N != 0 {
                // Re-use the space taken by the NULL terminator and swap it with the '.' separator.
                this.buf[this.n - 1] = b'.';
            }
        }

        this
    }

    /// Prepare the [`ModInfoBuilder`] for the next entry.
    ///
    /// This method acts as a separator between module firmware path entries.
    ///
    /// Must be called before constructing a new entry with subsequent calls to
    /// [`ModInfoBuilder::push`].
    ///
    /// See [`ModInfoBuilder::push`] for an example.
    pub const fn new_entry(self) -> Self {
        self.push_internal(b"\0")
            .push_module_name()
            .push_internal(b"firmware=")
    }

    /// Build the byte array.
    pub const fn build(self) -> [u8; N] {
        // Add the final NULL terminator.
        let this = self.push_internal(b"\0");

        if this.n == N {
            this.buf
        } else {
            crate::build_error!("Length mismatch.");
        }
    }
}

impl ModInfoBuilder<0> {
    /// Return the length of the byte array to build.
    pub const fn build_length(self) -> usize {
        // Compensate for the NULL terminator added by `build`.
        self.n + 1
    }
}