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

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

On 6/6/23 14:55, Peter Maydell wrote:
> 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.)

Thanks for this reference!

> 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.)

I see, thanks.