linux-kernel - Re: [GPIO] Crashed when not using

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Message-ID: <20120731064350.GD6004@arwen.pp.htv.fi>
Date:	Tue, 31 Jul 2012 09:43:51 +0300
From:	Felipe Balbi <balbi@...com>
To:	Kevin Hilman <khilman@...com>
Cc:	"Poddar, Sourav" <sourav.poddar@...com>,
	"DebBarma, Tarun Kanti" <tarun.kanti@...com>,
	lo <linux-omap@...r.kernel.org>,
	Santosh Shilimkar <santosh.shilimkar@...com>,
	Benoit Cousson <b-cousson@...com>,
	linux-kernel@...r.kernel.org, Felipe Balbi <balbi@...com>
Subject: Re: [GPIO] Crashed when not using

Hi,

On Mon, Jul 30, 2012 at 01:36:47PM -0700, Kevin Hilman wrote:

<little trimming>

> >>> The device tree data for acquiring the above GPIO interrupt line looks
> >>> like this.
> >>>
> >>> +++ linux-omap-storage/arch/arm/boot/dts/omap5-evm.dts  2012-07-30
> >>> 14:11:08.931694001 +0530
> >>> @@ -42,7 +42,8 @@
> >>>         tsl2771@39 {
> >>>                 compatible = "taos,tsl2771";
> >>>                 reg = <0x39>;
> >>> +                interrupt-parent = <&gpio5>;
> >>> +                interrupts = <21>; /* gpio line 149 */
> >>>         };
> >>>  };
> >>>
> >>> Note: using "gpio_request_one" in the driver solves the issue.
> >>> Is using this api in the driver required?
> >>> Any pointer on the above crash?
> >>
> > Hi Tarun,
> >> Any user/client driver of GPIO is supposed to go through
> >> gpio_request() API so that module clock
> >> is enabled correctly. Overriding of APIs would put the power
> >> management state machine in jeopardy.
> >> --
> > I tried putting "pm_runtime_get_sync" in gpio_irq_type api where the kernel
> > is crashing and the crash is no longer observed. So indeed, its about
> > enabling clocks.
> >
> > One doubt: Can't we put runtime apis in "gpio_irq_type" and eliminate
> > the use of
> > "gpio_request_one"??
> 
> No.
> 
> You must use the GPIO requiest/free APIs to tell the GPIO core that
> the GPIO line is in use.
> 
> Why do you want to avoid using gpio_request/gpio_free?

Then how do we differentiate from a driver perspective if e.g.
client->irq (for I2C client drivers) refers to a pin on a GPIO
controller or a real interrupt when running with DT ?

Having something like:

#interrupt-parent = &<gpio5>;
interrupts = <21>;

would already give me the correct IRQ number from the driver, now how do
we differentiate the interrupt parents ? There's no way to do that from
a driver perspective, so DT core has to either do it, or provide means
for drivers to detect it themselves.

-- 
balbi

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