Re: [PATCH] genirq: fix trigger flags check for shared irqs

[Brian Starkey]

On Thu, Jan 28, 2016 at 11:29:21AM +0100, Thomas Gleixner wrote:
> Brian,
>
> On Thu, 28 Jan 2016, Brian Starkey wrote:
> > On Tue, Jan 26, 2016 at 09:45:32PM +0100, Thomas Gleixner wrote:
> > > On Tue, 26 Jan 2016, Brian Starkey wrote:
> > >
> > > > For shared interrupts, if one requester passes in any IRQF_TRIGGER_*
> > > > flags whilst another doesn't, __setup_irq() can erroneously fail.
> > > >
> > > > The no-flags case should be treated as "already configured", so change
> > > > __setup_irq() to only check that the flags match if any have been
> > > > provided.
> > >
> > > What happens if that "already configured", i.e. the default setting, is
> > > conflicting with the newly requested interrupt?
> > >
> > > I rather prefer the failure than the resulting silent wreckage.
> > >
> >
> > Yes, I agree that would be best avoided. It seems to me that this case
> > is actually handled a bit lower down:
> >
> > 	} else if (new->flags & IRQF_TRIGGER_MASK) {
> > 		unsigned int nmsk = new->flags & IRQF_TRIGGER_MASK;
> > 		unsigned int omsk = irq_settings_get_trigger_mask(desc);
> >
> > 		if (nmsk != omsk)
> > 			/* hope the handler works with current  trigger mode
> > */
> > 			pr_warning("irq %d uses trigger mode %u; requested
> > %u\n",
> > 				   irq, nmsk, omsk);
> > 	}
> >
> > Perhaps that should be louder/fatal?
>
> Perhaps. So what's the actual problem case you are trying to solve?

I've got a few devices on the same interrupt line. One driver does
something along these lines:

	res = platform_get_resource(dev, IORESOURCE_IRQ, 0);
	flags = (res->flags & IRQF_TRIGGER_MASK) | IRQF_SHARED;
	request_irq(res->start, handler, flags, "name", dev);

This seems pretty reasonable. The problem is since 4a43d686fe33:
   of/irq: Pass trigger type in IRQ resource flags[1]
the trigger type information from device-tree is in res->flags.

So when the other drivers don't pass in any flags, they fail the check
in __setup_irq().

Changing the former driver to remove the flags doesn't seem right, and
adding flags to the latter would imply adding flags to _every_ driver,
which is an awful lot to change - and I'm not sure it would be possible
and/or effective in all cases.

Cheers,

-Brian

[1]http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=4a43d686fe336cc0e955c4400ba4d3fcff788786

> Thanks,
>
> 	tglx