Hi Linus, On Fri, Oct 30, 2015 at 12:03 PM, Linus Walleij <linus.walleij@xxxxxxxxxx> wrote: > There are a bunch of drivers that utilize the "ngpios" DT property > without any vendor prefix. Try to start cleaning up the mess by > defining what we mean by this property. > > Cc: devicetree@xxxxxxxxxxxxxxx > Cc: Pramod Kumar <pramodku@xxxxxxxxxxxx> > Cc: Jonas Gorski <jogo@xxxxxxxxxxx> > Signed-off-by: Linus Walleij <linus.walleij@xxxxxxxxxx> > --- > Documentation/devicetree/bindings/gpio/gpio.txt | 24 ++++++++++++++++++++++++ > 1 file changed, 24 insertions(+) > > diff --git a/Documentation/devicetree/bindings/gpio/gpio.txt b/Documentation/devicetree/bindings/gpio/gpio.txt > index 63b1b9039ce8..9b081e6143a0 100644 > --- a/Documentation/devicetree/bindings/gpio/gpio.txt > +++ b/Documentation/devicetree/bindings/gpio/gpio.txt > @@ -129,6 +129,30 @@ Every GPIO controller node must contain both an empty "gpio-controller" > property, and a #gpio-cells integer property, which indicates the number of > cells in a gpio-specifier. > > +Optionally, a GPIO controller may have a "ngpios" property. This property > +indicates the number of in-use slots of available slots for GPIOs. The > +typical example is something like this: the hardware register is 32 bits > +wide, but only 18 of the bits have a physical counterpart. The driver is > +generally written so that all 32 bits can be used, but the IP block is reused > +in a lot of designs, some using all 32 bits, some using 18 and some using > +12. In this case, setting "ngpios = <18>;" informs the driver that only the > +first 18 GPIOs, at local offset 0 .. 17, are in use. > + > +If these GPIOs do not happen to be the first N GPIOs at offset 0...N, an 0...N-1 > +additional bitmask is needed to specify which GPIOs are actually in use, > +and which are dummies. The bindings for this case has not yet been > +specified, but should be specified if/when such hardware appears. > + > +Example: > + > +gpio-controller@00000000 { > + compatible = "foo"; > + reg = <0x00000000 0x1000>; > + gpio-controller; > + #gpio-cells = <2>; > + ngpios = <18>; > +} The rcar-gpio driver uses the last number from the "gpio-ranges" to deduce the number of GPIOs to driver. Should this be changed? Thanks! Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds -- 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