From mboxrd@z Thu Jan  1 00:00:00 1970
From: vz@mleia.com (Vladimir Zapolskiy)
Date: Wed, 21 Dec 2016 05:30:21 +0200
Subject: [PATCH 1/3] dt: pwm: lpc32xx: add description of clocks and
 #pwm-cells properties
In-Reply-To: <015305d5-c22f-52da-9605-f2c19e3108b1@mleia.com>
References: <20161205014237.1689-1-vz@mleia.com>
 <20161205014237.1689-2-vz@mleia.com>
 <20161209214137.2hdugl5rmnwjrus4@rob-hp-laptop>
 <015305d5-c22f-52da-9605-f2c19e3108b1@mleia.com>
Message-ID: <5a865e27-e673-2f45-6c71-ca1e7d92a346@mleia.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

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@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.

Rob, have I managed to answer your questions?

If you accept my clarification, could you please ack the change?

--
With best wishes,
Vladimir