Re: [PATCH 2/2] hw/sd/allwinner-sdhost: Don't send non-boolean IRQ line levels

[Peter Maydell]

On Tue, 6 Jun 2023 at 13:39, Philippe Mathieu-Daudé <philmd@linaro.org> wrote:
>
> Hi Peter,
>
> On 6/6/23 12:46, Peter Maydell wrote:
> > QEMU allows qemu_irq lines to transfer arbitrary integers.  However
> > the convention is that for a simple IRQ line the values transferred
> > are always 0 and 1.  The A10 SD controller device instead assumes a
> > 0-vs-non-0 convention, which happens to work with the interrupt
> > controller it is wired up to.
> >
> > Coerce the value to boolean to follow our usual convention.
>
> I remember once wanting to convert qemu_set_irq() to take a boolean
> argument but someone said using integer was more useful because ...?
> I searched a bit but can't find that in my mail archives, maybe this
> was on IRC. Any clue? (I find simpler to use a boolean rather than
> having a convention of using integers restricted to [0, 1] range).

We have a lot of use cases where we just want to transfer a boolean
value between two devices. We have a few use cases where we want to
transfer an arbitrary integer across the channel between two devices.
(For instance hw/intc/etraxfs_pic.c:pic_update() sends a vector
number to the CPU via a qemu_irq -- see commit f4f643882d9dc467.)

At the moment we use qemu_irq() for both. In theory we could
construct a parallel set of machinery for wiring up and setting
values for the "want an integer" case and restrict qemu_irq() to
bool only, but the lazy path is to use the same function for both.
(If we had machinery that made it easy to construct arbitrary
strongly-typed signal connections, that might perhaps be ideal.
But it's probably not very easy especially in C.)

thanks
-- PMM