Re: [PATCH v6 3/6] rust: irq: add support for non-threaded IRQs and handlers

Alice Ryhl
2025-07-08T11:49:49Z

On Mon, Jul 07, 2025 at 10:30:27PM +0200, Benno Lossin wrote:
> On Mon Jul 7, 2025 at 6:18 PM CEST, Daniel Almeida wrote:
> > Alice,
> >
> > […]
> >
> >>> +/// The value that can be returned from an IrqHandler or a ThreadedIrqHandler.
> >>> +pub enum IrqReturn {
> >>> + /// The interrupt was not from this device or was not handled.
> >>> + None,
> >>> +
> >>> + /// The interrupt was handled by this device.
> >>> + Handled,
> >>> +}
> >>> +
> >>> +impl IrqReturn {
> >>> + fn into_inner(self) -> u32 {
> >>> + match self {
> >>> + IrqReturn::None => bindings::irqreturn_IRQ_NONE,
> >>> + IrqReturn::Handled => bindings::irqreturn_IRQ_HANDLED,
> >>
> >> One option is to specify these in the enum:
> >>
> >> /// The value that can be returned from an IrqHandler or a ThreadedIrqHandler.
> >> pub enum IrqReturn {
> >> /// The interrupt was not from this device or was not handled.
> >> None = bindings::irqreturn_IRQ_NONE,
> >>
> >> /// The interrupt was handled by this device.
> >> Handled = bindings::irqreturn_IRQ_HANDLED,
> >> }
> >
> > This requires explicitly setting #[repr(u32)], which is something that was
> > reverted at an earlier iteration of the series on Benno’s request.
>
> Yeah I requested this, because it increases the size of the enum to 4
> bytes and I think we should try to make rust enums as small as possible.
>
> @Alice what's the benefit of doing it directly in the enum?

Basically all uses of this enum are going to look like this:

fn inner() -> IrqReturn {
if !should_handle() {
return IrqReturn::None;
}
// .. handle the irq
IrqReturn::Handled
}

fn outer() -> u32 {
match inner() {
IrqReturn::None => bindings::irqreturn_IRQ_NONE,
IrqReturn::Handled => bindings::irqreturn_IRQ_HANDLED,
}
}

Setting the discriminant to the values ensures that the match in outer()
is a no-op. The enum is never going to be stored long-term anywhere so
its size doesn't matter.

Alice