From mboxrd@z Thu Jan 1 00:00:00 1970 From: Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= Subject: Re: [PATCH] gpio: document how to order GPIO controllers Date: Tue, 5 Jul 2016 20:04:47 +0200 Message-ID: <20160705180447.GP16643@pengutronix.de> References: <1467355333-8813-1-git-send-email-u.kleine-koenig@pengutronix.de> <20160705140546.GA10601@rob-hp-laptop> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Received: from metis.ext.4.pengutronix.de ([92.198.50.35]:43490 "EHLO metis.ext.4.pengutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755201AbcGESEx (ORCPT ); Tue, 5 Jul 2016 14:04:53 -0400 Content-Disposition: inline In-Reply-To: <20160705140546.GA10601@rob-hp-laptop> Sender: linux-gpio-owner@vger.kernel.org List-Id: linux-gpio@vger.kernel.org To: Rob Herring Cc: Linus Walleij , Alexandre Courbot , Mark Rutland , kernel@pengutronix.de, linux-gpio@vger.kernel.org, devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org On Tue, Jul 05, 2016 at 09:05:46AM -0500, Rob Herring wrote: > On Fri, Jul 01, 2016 at 08:42:13AM +0200, Uwe Kleine-K=F6nig wrote: > > This uses the same approach that is already used for spi, i2c and > > several other controllers to ensure a consistent numbering independ= ent > > of probe order. This is in use for several gpio drivers that alread= y now > > use of_alias_get_id(np, "gpio"). >=20 > Like SPI and I2C, I'm against further abuse of aliases for this purpo= se=20 > [1]. I considered spi and i2c the good examples here :-| > > Signed-off-by: Uwe Kleine-K=F6nig > > --- > > Hello, > >=20 > > Linus requested such a patch as part of a change that introduces > > this mechanism to the gpio-omap driver[1]. IMHO this is better done= in a > > separate patch, so here it comes. > >=20 > > Best regards > > Uwe > >=20 > > [1] http://thread.gmane.org/gmane.linux.kernel.gpio/17399/focus=3D1= 7629 > >=20 > > Documentation/devicetree/bindings/gpio/gpio.txt | 18 +++++++++++++= +++++ > > 1 file changed, 18 insertions(+) > >=20 > > diff --git a/Documentation/devicetree/bindings/gpio/gpio.txt b/Docu= mentation/devicetree/bindings/gpio/gpio.txt > > index 68d28f62a6f4..5dbacc8f094a 100644 > > --- a/Documentation/devicetree/bindings/gpio/gpio.txt > > +++ b/Documentation/devicetree/bindings/gpio/gpio.txt > > @@ -227,6 +227,24 @@ Example of two SOC GPIO banks defined as gpio-= controller nodes: > > #gpio-cells =3D <2>; > > }; > > =20 > > +Usually the GPIO banks in SoCs are ordered, that is there is a ded= icated "first > > +gpio bank". To fix this ordering in the device tree use aliases st= arting at 0 > > +(even if the first bank is called "GPIO1" in the hardware referenc= e). > > +This is necessary/handy to ensure deterministical numbering of GPI= Os and GPIO > > +controllers. >=20 > Why is deterministic numbering needed? in my case (with a pre 4.8 kernel) it's to control GPIO48 with /sys/class/gpio/gpio48. But also when using the gpio chardev device (that will hit 4.8-rc1 AFAIK) there is one device file per gpio chip. Now consider a user who wants to control/debug direction and value of GPIO48 (or GPIO2.16 for the chardev case). The strait forward approach is to use /sys/class/gpio/gpio48 (or /dev/dontknowthename2 with offset 16). I doubt there is a platform where it didn't work like this up to now and I'd consider it a userspace breakage to force the user to know that the 2nd gpio bank is located at address 0x53fd0000 and so to looku= p the gpio bank below /sys/bus/platform/devices/53fd0000.gpio/. On an i.MX25 device I currently see: root@hostname:/sys/bus/gpio/devices ls -l lrwxrwxrwx 1 root root 0 Jul 5 20:52 gpiochip0 -> .= =2E/../../devices/platform/soc/53f00000.aips/53f9c000.gpio/gpiochip0 lrwxrwxrwx 1 root root 0 Jul 5 20:52 gpiochip1 -> .= =2E/../../devices/platform/soc/53f00000.aips/53fa4000.gpio/gpiochip1 lrwxrwxrwx 1 root root 0 Jul 5 20:52 gpiochip2 -> .= =2E/../../devices/platform/soc/53f00000.aips/53fcc000.gpio/gpiochip2 lrwxrwxrwx 1 root root 0 Jul 5 20:52 gpiochip3 -> .= =2E/../../devices/platform/soc/53f00000.aips/53fd0000.gpio/gpiochip3 That is we have: Hardware name | software gpiochip GPIO4 | gpiochip0 GPIO3 | gpiochip1 GPIO1 | gpiochip2 GPIO2 | gpiochip3 I bet that's the probe order because when sorted by address (and so by order in the device tree) we have exactly this ordering. (Compare with $(grep gpio@ arch/arm/boot/dts/imx25.dtsi).) =46or a new interface this is OK, still I predict users will complain i= f the numbers used don't match naturally the hardware names. And IMHO the= y are right. Best regards Uwe --=20 Pengutronix e.K. | Uwe Kleine-K=F6nig = | Industrial Linux Solutions | http://www.pengutronix.de/= | -- To unsubscribe from this list: send the line "unsubscribe linux-gpio" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html