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From: David Brownell <david-b@pacbell.net>
To: "H Hartley Sweeten" <hartleys@visionengravers.com>
Subject: Re: [PATCH] gpiolib: add gpio_request/free_irq
Date: Tue, 9 Jun 2009 17:56:11 -0700
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On Tuesday 09 June 2009, H Hartley Sweeten wrote:
> On Friday, June 05, 2009 10:20 PM, David Brownell wrote:
> > On Friday 05 June 2009, H Hartley Sweeten wrote:
> > Add support functions to gpiolib to request/free gpio irqs.
> > 
> > I'm not keen on this.
> > 
> >  - At best it's a convenience layer ... for something that's
> >    not the least bit awkward to do otherwise.
> 
> 		... deletia ...
> 
> >  - Coupling it to gpiolib sort of defeats the point of saying
> >    that gpiolib is just an *implementation* of the interface.
> >    Where's the code to run for non-gpiolib platforms?
> > 
> 
> But if a driver is using the gpiolib interface calls wouldn't that
> prevent that driver from working on a platform that does not support
> gpiolib? File include/linux/gpio.h defines all the gpiolib calls to
> either return an error code or WARN_ON(1) when called.

There are three kinds of config to be concerned with:

 - Platform doesn't support the GPIO calls at all.  In those
   cases, drivers using <linux/gpio.h> get NOP stubs; you have
   this case covered.

 - Platforms supporting the calls but not using gpiolib.
   That's the case I pointed out -- you don't handle it.

 - Platforms supporting the calls with gpiolib.  This is the
   other case you handle.


> >  - Since it implicitly couples gpio_request() to a flavor of
> >    request_irq(), it precludes sharing those IRQs.
> > 
> 
> Can't the IRQ be shared by passing IRQF_SHARED as one of the flags?

Only one of them will be able to gpio_request(), so it
doesn't matter at all what you say to request_irq().


> > Basically, board setup can know that the GPIO is being used
> > as an IRQ, and do the request()/direction_input() before it
> > passes gpio_to_irq() to the driver. That's worked in every
> > case I've happened across so far...
> 
> I agree it works as-is right now.  I just thought this would be a
> convenient wrapper to handle a common setup step.  If it's overkill
> or not appropriate to add to gpiolib please disregard the patch.


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