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

[Brian Starkey]

On Thu, Jan 28, 2016 at 12:49:37PM +0100, Thomas Gleixner wrote:
> On Thu, 28 Jan 2016, Brian Starkey wrote:
> > I've got a few devices on the same interrupt line. One driver does
>
> Just for the record: When will hardware folks finally understand that shared
> interrupt lines are a nightmare?

In general, agreed. In this case though I think they get some grace - my
devices are all in an FPGA which only has one interrupt line to the SoC.

> > 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.
>
> So that commit does:
>
>   r->flags = IORESOURCE_IRQ | irqd_get_trigger_type(irq_get_irq_data(irq));
>
> which reads the current setting of the interrupt line.
>
> Now we pass exactly that to request_irq(). So first irq_of_parse_and_map()
> configures the interrupt type when mapping it and then hands in the same type
> information when requesting the irq.

Right, there's some redundancy here.

> I have no idea what the purpose of this is and the changelog of that commit is
> completely useless, sigh!
>
> I've cc'ed the author and the device tree folks. Perhaps are they able to
> explain what this commit tries to 'fix'.

This 'fix' is what makes me hit the problem - but even without it I
think the problem still exists.

It seems like in principle two drivers ought to be able to do

	request_irq(irq, handler, IRQF_SHARED | IRQF_TRIGGER_HIGH, ...);

and

	request_irq(irq, handler, IRQF_SHARED, ...);

without the latter call failing. Or do you disagree?

-Brian

> Thanks,
>
> 	tglx