Date:	Wed, 31 Jul 2013 13:29:26 +0200
From:	Tomasz Figa <tomasz.figa@...il.com>
To:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	linux-gpio@...r.kernel.org, Grant Likely <grant.likely@...aro.org>,
	Guennadi Liakhovetski <g.liakhovetski@....de>
Subject: Re: How to create IRQ mappings in a GPIO driver that doesn't control its IRQ domain ?

On Wednesday 31 of July 2013 13:11:33 Laurent Pinchart wrote:
> Hi Tomasz,
> 
> On Sunday 28 July 2013 12:07:48 Tomasz Figa wrote:
> > On Wednesday 24 of July 2013 01:21:44 Laurent Pinchart wrote:
> > > Hello,
> > > 
> > > I'm running into an issue on several Renesas SoC with IRQ domains and
> > > GPIOs.
> > > 
> > > On sh73a0, r8a73a4 and r8a7740, GPIOs and external interrupts are
> > > handled by two separate IP cores, namely the PFC (Pin Function
> > > Controller) and INTC (Interrupt Controller). The former is handled by
> > > the sh-pfc driver (drivers/pinctrl/sh-pfc) and the later by the
> > > irq-renesas-intc-irqpin driver (drivers/irqchip), referred to below as
> > > the irqpin driver.
> > 
> > Is the INTC used for anything more than just external interrupts on GPIO
> > lines?
> 
> Yes, it also handles other interrupt sources (NMI and peripherals), but
> those are not implemented now. The peripheral interrupts are also handled
> by the GIC, which is preferred over INTC.

OK, this is much more clear now.

> > > The sh73a0, for instance, has 32 external interrupt lines that are
> > > multiplexed on pins usable as GPIOs. Both the GPIO and external
> > > interrupt functions are usable at the same time, which allows reading
> > > the state of the interrupt lines.
> > > 
> > > These external interrupts are for MMC/SD support, among other devices.
> > > In this specific case the MMC/SD Card Detect signal is wired to one of
> > > the external interrupt signals, and the corresponding GPIO is passed to
> > > the MMC/SD controller driver. Depending on other configuration
> > > parameters the driver can then either poll the Card Detect signal, or
> > > register an interrupt handler to detect changes in the signal state.
> > > This features is implemented by the MMC/SD core, which call
> > > gpio_to_irq() on the GPIO to retrieve the corresponding IRQ number.
> > > 
> > > On non-DT systems the external IRQs are statically mapped at a known
> > > offset. The sh-pfc driver, to implement the gpio_to_irq() function
> > > (through its gpiochip .to_irq() handler), simply searches a
> > > SoC-specific lookup table for the fixed IRQ number associated with a
> > > given GPIO.
> > > 
> > > However, on DT systems, IRQs are mapped dynamically on demand. The
> > > irqpin driver registers a simple IRQ domain, and the
> > > irq_create_mapping() function can then be used to map a given IRQ,
> > > specified as an offset in the domain. This is where the problem
> > > appears, as the irqchip .to_irq() function is implemented in the sh-pfc
> > 
> > I assume it should be s/irqchip/gpiochip/ in the line above, shouldn't it?
> 
> Yes, my bad.

No problem.

> > > driver, which doesn't have access to the IRQ domain registered by the
> > > irqpin driver.
> > > 
> > > I could hack around this by exporting a function in the irqpin driver
> > > that would map an IRQ, and call that function from the sh-pfc driver.
> > > I'd rather avoid that solution as it would add a direct dependency
> > > between the two drivers.
> > 
> > If you could just get the IRQ domain registered by irqpin driver and use
> > it in sh-pfc, then I guess it would solve your problem, as you could
> > simply call irq_create_mapping() with the domain and hwirq as args in your
> > gpiochip .to_irq() callback.
> > 
> > I'm not sure if it's not a hack, but you could add a property to the node
> > of your pin controller that would contain a phandle to your interrupt
> > controller. Then you could use of_parse_phandle() to get to device node of
> > the INTC and then irq_find_host() to retrieve irq domain associated with
> > it.
> 
> That was my initial idea. However, one on of the SoCs, the GPIO interrupts
> are divided in two separate blocks, handled by two different interrupt
> controller instances. I could thus have a list of phandle + range, but that
> becomes pretty hackish. Specifying the interrupts explicitly would be more
> extensible.

Yes, in this case passing the domain alone makes little sense and domain + 
range would be a bit hackish indeed.

> > > Has anyone run into a similar issue ? My gut feeling is that the
> > > architecture isn't right somewhere, but I can't really pinpoint where.
> > > As the external IRQs are handled by an IP core separate from the PFC
> > 
> > Well, the fact that it's separate doesn't mean anything yet. Here my
> > question whether it's used exclusively for GPIO interrupts or not becomes
> > significant. If yes, maybe it could be simply moved to the pinctrl driver?
> 
> Depending on the SoC, I have two different IRQ controllers used for GPIO
> interrupts. They're called INTC and IRQC. INTC has other purposes (although
> not implemented at the moment). The IRQC instances used for GPIO interrupts
> are (at the moment) dedicated to GPIO interrupts, but other instances of the
> same IP core are used for other interrupts, so a separate driver makes
> sense in my opinion.

OK. So you need a bit smarter solution then.

Best regards,
Tomasz

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