Re: [PATCH v1 1/3] gpio: Add APM X-Gene standby GPIO controller driver

Linus Walleij
2014-10-29T09:52:48Z

On Fri, Oct 24, 2014 at 3:46 PM, Arnd Bergmann <arnd@arndb.de> wrote:
> On Friday 24 October 2014 14:14:43 Linus Walleij wrote:
>> On Wed, Oct 8, 2014 at 4:52 PM, Y Vo <yvo@apm.com> wrote:

>> > + apm_gc->irq = devm_kzalloc(&pdev->dev, sizeof(u32) * XGENE_MAX_GPIO_DS,
>> > + GFP_KERNEL);
>> > + if (!apm_gc->irq)
>> > + return -ENOMEM;
>> > + memset(apm_gc->irq, 0, sizeof(u32) * XGENE_MAX_GPIO_DS);
>> (...)
>> > + for (i = 0; i < apm_gc->nirq; i++) {
>> > + apm_gc->irq[default_pins[i]] = platform_get_irq(pdev, i);
>>
>> So the IRQs for all the GPIO pins are handled somewhere else instead
>> of being a cascaded IRQ controller.
>>
>> This means that the IRQ lines from each individual GPIO pin is
>> connected to a unique IRQ line on a secondary interrupt controller,
>> instead of the GPIO block being a cascaded interrupt controller
>> in its own right.
>>
>> Is this correct?
>
> See the discussion I had on this. Yes, each line is connected to a
> GIC SPI interrupt by itself. I've discussed this with Marc Zyngier
> and Thomas Gleixner at the conference last week, and we concluded
> that we will need a new generic interface to get data out of the
> parent interrupt controller in a proper way. The current implementation
> just maps the GIC registers and reads them directly, which of course
> is not a proper way to do it.

Hmmmmmm. OK shall we hold this driver until the infrastructure
issues are resolved?

The following is a recurring pattern among GPIO controllers:
the GPIO controller can go offline (asycnhcronous) and while it
is offline a secondary logic triggers an IRQ that wakes the system
up, however the GPIO logic cannot really "see" that IRQ since
it was sleeping when it arrived.

Thus a latent IRQ is pending in the wakeup logic. This concept
exists in drivers/pinctrl/nomadik/pinctrl-nomadik.c and I strongly
prefer to call these "latent irqs" as it's a clear unambigous
terminology.

So is this a case of latent IRQs pending in the GIC?

Yours,
Linus Walleij