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-König wrote: > > This uses the same approach that is already used for spi, i2c and > > several other controllers to ensure a consistent numbering independent > > of probe order. This is in use for several gpio drivers that already now > > use of_alias_get_id(np, "gpio"). > > Like SPI and I2C, I'm against further abuse of aliases for this purpose > [1]. I considered spi and i2c the good examples here :-| > > Signed-off-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx> > > --- > > Hello, > > > > 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. > > > > Best regards > > Uwe > > > > [1] http://thread.gmane.org/gmane.linux.kernel.gpio/17399/focus=17629 > > > > Documentation/devicetree/bindings/gpio/gpio.txt | 18 ++++++++++++++++++ > > 1 file changed, 18 insertions(+) > > > > diff --git a/Documentation/devicetree/bindings/gpio/gpio.txt b/Documentation/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 = <2>; > > }; > > > > +Usually the GPIO banks in SoCs are ordered, that is there is a dedicated "first > > +gpio bank". To fix this ordering in the device tree use aliases starting at 0 > > +(even if the first bank is called "GPIO1" in the hardware reference). > > +This is necessary/handy to ensure deterministical numbering of GPIOs and GPIO > > +controllers. > > 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 lookup 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 -> ../../../devices/platform/soc/53f00000.aips/53f9c000.gpio/gpiochip0 lrwxrwxrwx 1 root root 0 Jul 5 20:52 gpiochip1 -> ../../../devices/platform/soc/53f00000.aips/53fa4000.gpio/gpiochip1 lrwxrwxrwx 1 root root 0 Jul 5 20:52 gpiochip2 -> ../../../devices/platform/soc/53f00000.aips/53fcc000.gpio/gpiochip2 lrwxrwxrwx 1 root root 0 Jul 5 20:52 gpiochip3 -> ../../../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).) For a new interface this is OK, still I predict users will complain if the numbers used don't match naturally the hardware names. And IMHO they are right. Best regards Uwe -- Pengutronix e.K. | Uwe Kleine-König | Industrial Linux Solutions | http://www.pengutronix.de/ | -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
