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Message-ID: <20250306222336.23482-3-dakr@kernel.org>
Date: Thu, 6 Mar 2025 23:23:28 +0100
From: Danilo Krummrich <dakr@...nel.org>
To: airlied@...il.com,
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Danilo Krummrich <dakr@...nel.org>
Subject: [PATCH v6 2/5] rust: firmware: introduce `firmware::ModInfoBuilder`
The `firmware` field of the `module!` only accepts literal strings,
which is due to the fact that it is implemented as a proc macro.
Some drivers require a lot of firmware files (such as nova-core) and
hence benefit from more flexibility composing firmware path strings.
The `firmware::ModInfoBuilder` is a helper component to flexibly compose
firmware path strings for the .modinfo section in const context.
It is meant to be used in combination with `kernel::module_firmware!`.
Co-developed-by: Alice Ryhl <aliceryhl@...gle.com>
Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
Signed-off-by: Danilo Krummrich <dakr@...nel.org>
---
rust/kernel/firmware.rs | 127 ++++++++++++++++++++++++++++++++++++++++
1 file changed, 127 insertions(+)
diff --git a/rust/kernel/firmware.rs b/rust/kernel/firmware.rs
index c5162fdc95ff..6008b62f2de8 100644
--- a/rust/kernel/firmware.rs
+++ b/rust/kernel/firmware.rs
@@ -115,3 +115,130 @@ 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 {}
+
+/// 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`].
+ ///
+ /// # Example
+ ///
+ /// ```
+ /// 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.as_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
+ }
+}
--
2.48.1
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