Re: [PATCH V6 2/2] virtio-gpio: Add support for interrupts

[Arnd Bergmann <arnd@kernel.org>]

On Tue, Jul 27, 2021 at 8:23 AM Viresh Kumar <viresh.kumar@linaro.org> wrote:
> On 26-07-21, 14:13, Arnd Bergmann wrote:
> > The question is whether it adds any value though. As far as I can tell,
> > it is completely redundant, duplicating either what is implied by
> > irq type==none, or what is implied by the request not being queued.
>
> Right, we shouldn't have redundant stuff in here.
>
> Though, binding of all interrupt operations to the eventq can be trick
> IMO.
>
> - How will the driver mask an interrupt for which the buffer is
>   already sent over the eventq? There is no API available to recall a
>   buffer. So we would need an API over the requestq for that.

Agreed, there needs to be some way to cancel the request. I don't
think this would have to be a fast or common operation, so setting
the line back to IRQ_TYPE_NONE would be one way.

Another option would be to make the mask software-only and
just ignore an incoming event for a line that is configured as
masked, and then not requeue the request.

> - Latching of edge interrupt between the buffer is returned by the
>   device and requeued by the driver. How will the device know if the
>   user has simply requeued the eventq buffer (where the latched value
>   is meaningful) or it has done something like free_irq() followed by
>   request_irq() in the kernel (where the latched value must be
>   discarded).

I was expecting a 'mask' to not discard the latched event but simply
not deliver it until it gets unmasked. Either way, we can define that
a new set-irq-type request discards all latched edge interrupts.

       Arnd