Re: [PATCH v4 3/3] Input: gpio_keys.c: Enable use with non-local GPIO chips.

[David Jander <david.jander@protonic.nl>]

On Fri, 16 Mar 2012 01:32:01 -0700
Dmitry Torokhov <dmitry.torokhov@gmail.com> wrote:

> On Fri, Mar 16, 2012 at 09:17:01AM +0100, David Jander wrote:
> > On Fri, 16 Mar 2012 00:20:04 -0700
> > Dmitry Torokhov <dmitry.torokhov@gmail.com> wrote:
> > 
> > > Hi David,
> > > 
> > > On Tue, Jun 14, 2011 at 11:08:11AM +0200, David Jander wrote:
> > > > Use a threaded interrupt handler in order to permit the handler to use
> > > > a GPIO driver that causes things like I2C transactions being done inside
> > > > the handler context.
> > > > Also, gpio_keys_init needs to be declared as a late_initcall, to make sure
> > > > all needed GPIO drivers have been loaded if the drivers are built into the
> > > > kernel.
> > > 
> > > Don't want to resurrect the whole initcall discussion, but could you
> > > tell me again why the interrup handler needs to be threaded? We do not
> > > access hardware from it, hardware is accessed from workqueue context.
> > > Here is the ISR in its entirety:
> > 
> > Sorry, the reason described is apparently not very clear. The real reason seems
> > to be that I would like this driver to work with I2C GPIO expanders, and its
> > the GPIO expanders "interrupt controller" which has itself a threaded handler
> > (due to I2C transfers done in it to ack an IRQ). So this is actually a nested
> > and threaded interrupt controller (because the IRQ line of the GPIO expander
> > is connected to a different GPIO acting itself also as interrupt line).
> > In irq/manage.c, function __setup_irq():
> > 
> > ...
> > 	/*
> > 	 * Check whether the interrupt nests into another interrupt
> > 	 * thread.
> > 	 */
> > 	nested = irq_settings_is_nested_thread(desc);
> > 	if (nested) {
> > 		if (!new->thread_fn) {
> > 			ret = -EINVAL;
> > 			goto out_mput;
> > 		}
> > ...
> > 
> > This is were requesting a non-threaded IRQ from this GPIO controller will fail.
> > 
> > I know this is not a trivial setup, but IMHO it is very useful (for
> > connecting keyboards), and a nice demonstration of the powerful features this
> > GPIO driver has :-)
> 
> Thanks for the explanation of your setup.
> 
> > 
> > > static irqreturn_t gpio_keys_isr(int irq, void *dev_id)
> > > {
> > >         struct gpio_button_data *bdata = dev_id;
> > >         const struct gpio_keys_button *button = bdata->button;
> > > 
> > >         BUG_ON(irq != gpio_to_irq(button->gpio));
> > > 
> > >         if (bdata->timer_debounce)
> > >                 mod_timer(&bdata->timer,
> > >                         jiffies + msecs_to_jiffies(bdata->timer_debounce));
> > >         else
> > >                 schedule_work(&bdata->work);
> > > 
> > >         return IRQ_HANDLED;
> > > }
> > > 
> > > It looks to me that non-threaded handler would work as well? Or
> > > gpio_to_irq() can sleep with certain chips?
> > 
> > Not in my case. I just checked again. If I change request_threaded_irq() to
> > request_irq(), I get this:
> > 
> > ...
> > [    6.409810] gpio-keys gpio_keys.0: Unable to claim irq 0; error -22
> > [    6.416106] gpio-keys: probe of gpio_keys.0 failed with error -22
> > ...
> > 
> > This error -22 (-EINVAL) is returned from __setup_irq() (see above).
> 
> But the original code used request_any_context_irq() which should have
> taken care of your nested IRQ setup:

Hmm. You are right. Apparently this change was introduced in 2.6.38, and I
must have missed it. Before 2.6.38, this place called request_irq(), which was
broken for my case.

I just checked, and indeed, using request_any_context_irq() seems to work fine
for me.

Best regards,

-- 
David Jander
Protonic Holland.