On Wed, Mar 05, 2025 at 10:30:31PM +0000, Benno Lossin wrote:
> On Tue Mar 4, 2025 at 6:34 PM CET, Danilo Krummrich wrote:
> > 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!`,
> > which is introduced in a subsequent patch.
> >
> > Co-developed-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>
> > Signed-off-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>
> > Signed-off-by: Danilo Krummrich <dakr@xxxxxxxxxx>
> > ---
> > rust/kernel/firmware.rs | 98 +++++++++++++++++++++++++++++++++++++++++
> > 1 file changed, 98 insertions(+)
> >
> > diff --git a/rust/kernel/firmware.rs b/rust/kernel/firmware.rs
> > index c5162fdc95ff..6e6972d94597 100644
> > --- a/rust/kernel/firmware.rs
> > +++ b/rust/kernel/firmware.rs
> > @@ -115,3 +115,101 @@ 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.
> > +///
> > +/// It is meant to be used in combination with [`kernel::module_firmware!`].
> > +///
> > +/// For more details and an example, see [`kernel::module_firmware!`].
> > +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.
> > + ///
> > + /// After a new [`ModInfoBuilder`] instance has been created, [`ModInfoBuilder::prepare`] must
> > + /// be called before adding path components.
> > + pub const fn push(self, s: &str) -> Self {
> > + if N != 0 && self.n == 0 {
> > + crate::build_error!("Must call prepare() before push().");
>
> This will only prevent the first `prepare` call being missed, right?
Correct, unfortunately there's no way to detect subsequent ones.
>
> > + }
> > +
> > + self.push_internal(s.as_bytes())
> > + }
> > +
> > + const fn prepare_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.push_internal(b"firmware=")
> > + }
> > +
> > + /// Prepare for the next module info entry.
> > + ///
> > + /// Must be called before [`ModInfoBuilder::push`] can be called.
>
> If you always have to call this before `push`, why not inline it there?
You can push() multiple times to compose the firmware path string (which is the
whole purpose :).
Example from nova-core:
pub(crate) struct ModInfoBuilder<const N: usize>(firmware::ModInfoBuilder<N>);
impl<const N: usize> ModInfoBuilder<N> {
const fn make_entry_file(self, chipset: &str, fw: &str) -> Self {
let version = "535.113.01";
ModInfoBuilder(
self.0
.prepare()
.push("nvidia/")
.push(chipset)
.push("/gsp/")
.push(fw)
.push("-")
.push(version)
.push(".bin"),
)
}
const fn make_entry_chipset(self, chipset: &str) -> Self {
self.make_entry_file(chipset, "booter_load")
.make_entry_file(chipset, "booter_unload")
.make_entry_file(chipset, "bootloader")
.make_entry_file(chipset, "gsp")
}
pub(crate) const fn create(
module_name: &'static kernel::str::CStr,
) -> firmware::ModInfoBuilder<N> {
let mut this = Self(firmware::ModInfoBuilder::new(module_name));
let mut i = 0;
while i < gpu::Chipset::NAMES.len() {
this = this.make_entry_chipset(gpu::Chipset::NAMES[i]);
i += 1;
}
this.0
}
}
