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

[Danilo Krummrich <dakr@redhat.com>]

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@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