Re: [RFC PATCH 0/3] If an IRQ is a GPIO, request and configure it

[Russell King - ARM Linux <linux@arm.linux.org.uk>]

On Fri, Aug 05, 2011 at 12:33:31PM -0700, Stephen Warren wrote:
> Russell King - ARM Linux wrote at Friday, August 05, 2011 1:15 PM:
> > On Fri, Aug 05, 2011 at 08:43:20AM -0700, Stephen Warren wrote:
> > > Russell King - ARM Linux wrote at Friday, August 05, 2011 3:40 AM:
> > > > On Thu, Aug 04, 2011 at 05:00:17PM -0600, Stephen Warren wrote:
> > > > > In http://www.spinics.net/lists/linux-tegra/msg01731.html, Mark Brown
> > > > > pointed out that it was a little silly forcing every board or driver
> > > > > to gpio_request() a GPIO that is later converted to an IRQ, and passed
> > > > > to request_irq. The first patch in this series instead makes the core
> > > > > IRQ code perform these calls when appropriate, to avoid duplicating it
> > > > > everywhere.
> > > >
> > > > Trying to go from IRQ to GPIO is not a good idea - most of the
> > > > IRQ <-> GPIO macros we have today are just plain broken.  Many of them
> > > > just add or subtract a constant, which means non-GPIO IRQs have an
> > > > apparant GPIO number too.  Couple this with the fact that all positive
> > > > GPIO numbers are valid, and this is a recipe for wrong GPIOs getting
> > > > used and GPIOs being requested for non-GPIO IRQs.
> > > >
> > > > I think this was also discussed in the past, and the conclusion was that
> > > > IRQs should be kept separate from GPIOs.  Maybe views have changed since
> > > > then...
> > > >
> > > > However, if we do want to do this, then it would be much better to provide
> > > > a new API for requesting GPIO IRQs, eg:
> > > >
> > > > gpio_request_irq()
> > > >
> > > > which would wrap around request_threaded_irq(), takes a GPIO number,
> > > > does the GPIO->IRQ conversion internally, and whatever GPIO setup is
> > > > required.  Something like this:
> > >
> > > With that approach, drivers need to explicitly know whether they're
> > > passed a GPIO or an IRQ, and do something different, or they need to
> > > choose to only accept a GPIO or IRQ.
> > 
> > You completely missed the biggest reason why your approach is broken.
> 
> No, I didn't.

Yes you did.

> I was discussing whether an alternative API for IRQ registration
> would work, and I was pointing out some problems with it.
> 
> That has nothing to do with whether my original proposal is workable.

And that proves that you missed the point.  I am suggesting an alternative
solution precisely because your original proposal is unworkable.