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

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Message-ID: <CAMQu2gxXX+4gtKVnAMMK4qr9ihJuP-OwjOYgr=6VrGZ2DWSf2A@mail.gmail.com>
Date:	Tue, 31 Jul 2012 14:32:43 +0200
From:	"Shilimkar, Santosh" <santosh.shilimkar@...com>
To:	balbi@...com
Cc:	"Poddar, Sourav" <sourav.poddar@...com>,
	Kevin Hilman <khilman@...com>,
	"DebBarma, Tarun Kanti" <tarun.kanti@...com>,
	lo <linux-omap@...r.kernel.org>,
	Benoit Cousson <b-cousson@...com>, linux-kernel@...r.kernel.org
Subject: Re: [GPIO] Crashed when not using

On Tue, Jul 31, 2012 at 8:52 AM, Felipe Balbi <balbi@...com> wrote:
>
> Hi,
>
> On Tue, Jul 31, 2012 at 10:23:16AM +0530, Poddar, Sourav wrote:
> > >>>> 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.
> > >
> > Thanks for this confirmation.
> > > Why do you want to avoid using gpio_request/gpio_free?
> > >
> > I was assuming that DT based gpio IRQ registration will automatically
> > take care of
> > the above APIs. But since that is not the case(as mentioned by
> > santosh),  we need to use the
> > gpio_request/free apis.
>
> Hang on for a while, let's try to get to the bottom of this debate first
> ;-)
>
> We have a canonical way of passing IRQ numbers to drivers through DT and
> that is the "interrupts" attribute. It shouldn't matter if that IRQ pin
> is connected to a real IRQ line or through a GPIO controller. In both
> cases we should use the "interrupts" attribute.
>
> If DT core doesn't allocate the GPIO for us then how does this work:
>
> (omap4-sdp.dts)
>
> 127 &mcspi1 {
> 128         eth@0 {
> 129                 compatible = "ks8851";
> 130                 spi-max-frequency = <24000000>;
> 131                 reg = <0>;
> 132                 interrupt-parent = <&gpio2>;
> 133                 interrupts = <2>; /* gpio line 34 */
> 134                 vdd-supply = <&vdd_eth>;
> 135         };
> 136 };
>
>
> There's no gpio request on the driver:
>
> $ git grep -e gpio_request drivers/net/ethernet/micrel/ks8851.c
> $
>
> Since Benoit was the one who added that to the dts file (commit
> e7c64db9), I assume he tested his patch before posting, so again I ask -
> How does that work and why doesn't this work for Sourav's tsl2771
> controller ?
>
> This is either a regression on drivers/of, or commit e7c64db9 is also
> broken...
>
> Benoit, do you know how should this work ?
>
I had a discussion with Benoit on this. In fact there is a way to actually
trigger the GPIO request.

> 132                 interrupt-parent = <&gpio2>;
> 133                 interrupts = <2>; /* gpio line 34 */

As above you can see, GPIO2 bank and 2nd line.
And then it will make use of gpio_irq chip properties
to probe the GPIO line.

Saurabh can try this out for his use case.

Regards
Santosh
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