linux-kernel - Re: [PATCH 3/3] regmap: enhance regmap-irq to handle 1 IRQ feeding n chips

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Date:	Tue, 31 Jul 2012 17:18:36 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
CC:	Liam Girdwood <lrg@...com>, linux-kernel@...r.kernel.org,
	Samuel Ortiz <sameo@...ux.intel.com>,
	Stephen Warren <swarren@...dia.com>
Subject: Re: [PATCH 3/3] regmap: enhance regmap-irq to handle 1 IRQ feeding
 n chips

On 07/30/2012 11:25 AM, Mark Brown wrote:
> On Mon, Jul 30, 2012 at 11:00:04AM -0600, Stephen Warren wrote:
>> On 07/29/2012 02:36 PM, Mark Brown wrote:
>>> On Fri, Jul 27, 2012 at 01:01:56PM -0600, Stephen Warren wrote:
> 
>> I had implemented this in regmap since you'd specifically mentioned
>> doing that. If I convert the code not to use separate IRQ domains for
> 
> I think what I'd said was that we should factor it out rather than that
> it should be specifically done in regmap.
> 
>> this, would that be acceptable?
> 
> Probably.

The more I think about this, the more I prefer the way the way it is in
the patch I posted.

I don't think it's appropriate to put this support into the IRQ core.
The main issue is that all the handlers for any shared wired-or
interrupt line have to be registered before the IRQ is enabled, to avoid
some initially active interrupt continually firing before the IRQ is
enabled. Co-ordinating this when the wired-or line is on a board outside
a device driver rather than internal to a chip and one device driver is
a bit more than the IRQ core should probably be doing, hence I imagine
why it doesn't support it.

Co-ordinating this setup where all the sources of the wired-or are in
one chip seems to belong to the chip driver, which is where my patch did
this.

I guess I could modify regmaps_irq_thread() so that instead of:

	for (i = 0; i < d->nchips; i++)
		handle_nested_irq(irq_find_mapping(d->irqdom, i));

... it short-circuited and instead did something like:

	for (i = 0; i < d->nchips; i++)
		regmap_irq_thread(irq_find_mapping(d->irqdom, i),
			d->datas[i]);

but it seems a little hokey to short-circuit the IRQ core; it would
prevent execution of any statistics gathering or stuck interrupt
handling that handle_nested_irq() might do for example.

Now, if we made each child regmap_irq not be its own IRQ domain or
irq_chip, but simply had one top-level domain/chip that aggregated them,
that argument would be moot. However, that top-level domain/chip would
become rather complex and just end up doing a bunch of demultiplexing
code that's not needed if we do it like in my patch...
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