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

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Date:	Thu, 30 Jan 2014 22:32:32 +0100
From:	Steffen Trumtrar <s.trumtrar@...gutronix.de>
To:	delicious quinoa <delicious.quinoa@...il.com>
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>,
	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 03:15:11PM -0600, delicious quinoa wrote:
> 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'?

I meant gpio drivers (at least the ones I have used).

> 
> 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.
> 

Hm, okay...for GPIOs I'm with you. But when I specify a gpio as
interrupt for a device, I have to first export it manually before I can
use the device? Sounds weird.

Steffen

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