linux-kernel - Re: [PATCH] RFC: interrupt consistency check for OF GPIO IRQs

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Message-ID: <2966898.neCKEkcf1e@avalon>
Date:	Fri, 06 Sep 2013 17:32:43 +0200
From:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:	Linus Walleij <linus.walleij@...aro.org>
Cc:	Grant Likely <grant.likely@...aro.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Alexander Holler <holler@...oftware.de>,
	Linux-OMAP <linux-omap@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Javier Martinez Canillas <javier.martinez@...labora.co.uk>,
	Enric Balletbo i Serra <eballetbo@...il.com>,
	Jean-Christophe PLAGNIOL-VILLARD <plagnioj@...osoft.com>,
	Santosh Shilimkar <santosh.shilimkar@...com>,
	Kevin Hilman <khilman@...aro.org>,
	Balaji T K <balajitk@...com>,
	Tony Lindgren <tony@...mide.com>,
	Jon Hunter <jgchunter@...il.com>
Subject: Re: [PATCH] RFC: interrupt consistency check for OF GPIO IRQs

Hi Linus,

Sorry for the late reply.

On Thursday 22 August 2013 00:02:39 Linus Walleij wrote:
> On Tue, Aug 20, 2013 at 12:04 AM, Laurent Pinchart wrote:
> > On Wednesday 31 July 2013 01:44:53 Linus Walleij wrote:
> >> I don't see how sharing works here, or how another user, i.e. another one
> >> than the user wanting to recieve the IRQ, can validly request such a
> >> line? What would the usecase for that valid request be?
> > 
> > When the GPIO is wired to a status signal (such as an MMC card detect
> > signal) the driver might want to read the state of the signal
> > independently of the interrupt handler.
> 
> That is true. But for such a complex usecase I think it's reasonable that
> we only specify the GPIO in the device tree, and the driver utilizing the
> IRQ need to take that and perform gpio_to_irq() on it, and then it still
> works to use it both ways.

I'm pretty sure I would have had an objection a couple of weeks ago when I was 
looking into this, but I can't think of another use case for now, so I agree 
with you.

> >> Basically I believe these two things need to be exclusive in the DT
> >> world:
> >> 
> >> A: request_irq(a resource passed from "interrupts");
> >>      -> core implicitly performs gpio_request()
> >>          gpio_direction_input()
> >> 
> >> B: gpio_request(a resource passed from "gpios");
> >>      gpio_direction_input()
> >>      request_irq(gpio_to_irq())
> >> 
> >> Never both. And IIUC that was what happened in the OMAP case.
> > 
> > Isn't the core issue that we can translate a GPIO number to an IRQ number,
> > but not the other way around ? If that could be done, we could request
> > the GPIO and configure it as an input when the IRQ is requested.
> 
> That is true. It would be easier if all GPIO drivers has an irqchip and
> and irqdomain, then we could implement irq_to_gpio() properly in gpiolib
> and this would not be a problem. Alas, not all do.
> 
> But I also think that the DT contains (as demonstrated by the patch)
> all information about what interrupts and GPIOs may conflict, so I
> also see this as something of a consistency check, but it could go
> in either way.

-- 
Regards,

Laurent Pinchart
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