On 12/10/2016 01:51 AM, Vladimir Zapolskiy wrote: > Hi Rob, > > On 12/09/2016 11:41 PM, Rob Herring wrote: >> On Mon, Dec 05, 2016 at 03:42:37AM +0200, Vladimir Zapolskiy wrote: >>> NXP LPC32xx SoCs have two simple independent PWM controllers with a single >>> output each, in this case there is no need to specify PWM channel argument >>> on client side, one cell for setting PWM output frequency is sufficient. >>> >>> Another added to the description property 'clocks' has a standard meaning >>> of a controller supply clock, in the LPC32xx User's Manual the clock is >>> denoted as PWM1_CLK or PWM2_CLK clock. >>> >>> Signed-off-by: Vladimir Zapolskiy <vz@xxxxxxxxx> >>> --- >>> Documentation/devicetree/bindings/pwm/lpc32xx-pwm.txt | 7 +++++++ >>> 1 file changed, 7 insertions(+) >>> >>> diff --git a/Documentation/devicetree/bindings/pwm/lpc32xx-pwm.txt b/Documentation/devicetree/bindings/pwm/lpc32xx-pwm.txt >>> index 74b5bc5..523d796 100644 >>> --- a/Documentation/devicetree/bindings/pwm/lpc32xx-pwm.txt >>> +++ b/Documentation/devicetree/bindings/pwm/lpc32xx-pwm.txt >>> @@ -3,15 +3,22 @@ LPC32XX PWM controller >>> Required properties: >>> - compatible: should be "nxp,lpc3220-pwm" >>> - reg: physical base address and length of the controller's registers >>> +- clocks: clock phandle and clock specifier pair >>> +- #pwm-cells: should be 1, the cell is used to specify the period in >>> + nanoseconds. >> >> This use of the cell is a bit odd as the period is s/w config and this >> would typically be a channel selection or such. > > this is a classic PWM channel configuration property for PWM consumers > described in DT, for instance PWM frequency for display panel backlight > on boot. > > I think >90% of PWM controllers with device tree bindings have this > argument in #pwm-cells, from bindings/pwm/pwm.txt : > > pwm-specifier typically encodes the chip-relative PWM number and > the PWM period in nanoseconds. > > You also may skim through phandle arguments of 'pwms' property, > commonly the second argument is the requested frequency. > > In this particular case I just drop PWM channel number, because > the LPC32xx PWM controller has a single output channel. > >> What if I want user specified/changed periods? >> > > The preset period still can be changed over sysfs in runtime. Rob, have I managed to answer your questions? If you accept my clarification, could you please ack the change? -- With best wishes, Vladimir -- 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
