[PATCH 1/3] dt: pwm: lpc32xx: add description of clocks and #pwm-cells properties

[Vladimir Zapolskiy]

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 at mleia.com>
>> ---
>>  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.

--
With best wishes,
Vladimir