Subject: [PATCH 2/2] gpio/tegra: Dynamically allocate IRQ base, and support DT

From: [email-masked] (Rob Herring)
Date: Mon, 05 Dec 2011 07:35:16 -0600

Shawn,

On 12/05/2011 12:55 AM, Shawn Guo wrote:
> On Wed, Nov 30, 2011 at 05:45:36PM -0700, Stephen Warren wrote:
> [...]
>>  static void tegra_gpio_irq_ack(struct irq_data *d)
>>  {
>> -	int gpio = d->irq - INT_GPIO_BASE;
>> +	int gpio = d->hwirq;
>>  
> Though it's working right now, I'm not sure it's safe enough.  This
> only works when d->hwirq_base is 0, which is true for now.  But I doubt
> it will be always true.  I guess hwirq_base was introduced there for
> some reason.  When some day irqdomain starts using this field, the
> above code starts being broken.  IMO, the way that generic-chip.c is
> using to calculate the number, d->irq - gc->irq_base, is much more
> safer.

It does work as the GIC hwirq_base is non-zero. It was introduced
exactly so that no conversion of hwirq is needed for functions like
this. hwirq_base is the starting point local to the controller
numbering. Say you have gpio controller with 16 lines, but only the
upper 8 lines have interrupt capability. Then you would set hwirq_base
to 8 and nr_irq to 8. Then hwirq will always be set to 8-15.

Rob