Re: question on generic gpio interface

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Hi David,

Thanks for your detailed answer, it helps a lot !

On 4/14/07, David Brownell <[email protected]> wrote:
On Friday 13 April 2007 1:51 pm, Francis Moreau wrote:
> Hi,
>
> I'm trying to port my old gpio code to the generic one to see if it
> can fit my needs.

Good .. this is more like an IRQ question though.


yeah now it appears to me so...


> The gpio controller is a home made one and has a really weird
> interface. It has several registers to read the gpio status, to
> configure gpio directions, or to configure if a gpio can trigger an
> interrupt and on which event (level or edge). All gpios use the same
> IRQ and a gpio controller register allows to read which gpio has
> triggered the interrupt.

I'll trust you on "weird", but that sounds quite typical in
terms of functionality.  You'll find that most system-on-chip
GPIO controllers act the same way.

IRQ logic on that platform must do a few things, like:

 - NR_IRQS includes the N interrupts triggered from that chip,
   and their numbers probably fit right sometimes after the
   core set of IRQs (which might include SOC GPIO irqs);

 - You'll provide an irq_chip for this controller, and it will
   handle the relevant irq operations (set trigger type, mask,
   unmask etc);

 - When configuring the IRQ handler for that "same IRQ", you'll
   set it up to use a chained handler that you provide, which
   reads the register to see which gpio(s) triggered the IRQ,
   maybe acks it (if just reading that register isn't enough),
   and then calls whatever handler was instaled for that GPIO.

If that's not familiar to you, look at arch/arm/mach-at91/gpio.c
or arch/arm/mach-pxa/irq.c or arch/arm/plat-omap/gpio.c or a
number of other similar files showing how the "toplevel" IRQ
logic will demux from a "one of these N GPIOs" interrupt down
to the handler for that particular IRQ.


I think I got the picture now, thanks again.

Just to be sure I understand, it seems to me that your point 2) and 3)
are 2 different approaches to do the same thing, aren't they ?

If so I can only implement 2) since it seems to me better than the
last one (it better uses genirq layer).

Thanks !
--
Francis
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