linux-kernel - Re: [PATCH v9] gpio: add a driver for Synopsys DesignWare APB GPIO

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Date:	Thu, 30 Jan 2014 15:15:11 -0600
From:	delicious quinoa <delicious.quinoa@...il.com>
To:	Steffen Trumtrar <s.trumtrar@...gutronix.de>
Cc:	Linus Walleij <linus.walleij@...ricsson.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	Jamie Iles <jamie@...ieiles.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	Rob Herring <rob.herring@...xeda.com>,
	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
	Heiko Stuebner <heiko@...ech.de>, Alan Tull <atull@...era.com>,
	Dinh Nguyen <dinguyen@...era.com>,
	Yves Vandervennet <rocket.yvanderv@...il.com>
Subject: Re: [PATCH v9] gpio: add a driver for Synopsys DesignWare APB GPIO

On Thu, Jan 30, 2014 at 2:50 PM, Steffen Trumtrar
<s.trumtrar@...gutronix.de> wrote:
> Hi!
>
> On Thu, Jan 30, 2014 at 01:40:04PM -0600, delicious quinoa wrote:
>> On Thu, Dec 12, 2013 at 3:08 AM, Steffen Trumtrar
>> <s.trumtrar@...gutronix.de> wrote:
>>
>> > Second: The interrupt is registered as "GIC 37", which is a real interrupt on
>> > the Socfpga. I would expect it to be marked as "GPIO 2xx" (or something in that
>> > range). The interrupt from the gpiochip itself isn't registered at all ?!
>>
>> Hi Stephen,
>>
>> Did you export the gpio lines and set the edge in sysfs?  Because the
>> interrupts aren't allocated otherwise.
>>
>> For instance:
>>
>> root@...fpga_cyclone5:~# echo 195 > /sys/class/gpio/export
>> root@...fpga_cyclone5:~# echo rising > /sys/class/gpio/gpio195/edge
>>
>> Now I can see a pretty nicely named interrupt in /proc/interrupts:
>>
>> 256:          0          0  gpio-dwapb  24  gpiolib
>>
>
> I didn't try that and I think this behaviour is pretty uncommon.
> This should be fixed in the driver. I never wrote a gpiochip-driver,
> so I don't know what is missing, but maybe just some functioncall ?!
> All other drivers I came across have that entry from probing without
> any fiddling.

Hi Steffen,

Do you mean 'all other gpio drivers' or 'all other non-gpio drivers'?

This is the behavior that is implemented in the community gpio
framework drivers/gpio/gpiolib.c, not anything special implemented in
this dw gpio driver.

It's documented in Documentation/gpio/sysfs.txt and
Documentation/ABI/testing/sysfs-gpio.

You get userspace control of a gpio by 'export'ing it in sysfs.  And
then by default, the interrupt edge is set to 'none' (no irq) until
you set the edge in sysfs.

Alan

>
> Thanks,
> Steffen
>
> --
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