linux-kernel - Re: [PATCH v2 11/16] pwm: add documentation for PWM modes

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Date:   Mon, 22 Jan 2018 10:55:43 +0200
From:   Claudiu Beznea <Claudiu.Beznea@...rochip.com>
To:     Rob Herring <robh@...nel.org>
CC:     <thierry.reding@...il.com>, <mark.rutland@....com>,
        <linux@...linux.org.uk>, <daniel@...que.org>,
        <haojian.zhuang@...il.com>, <robert.jarzmik@...e.fr>,
        <corbet@....net>, <nicolas.ferre@...rochip.com>,
        <alexandre.belloni@...e-electrons.com>,
        <linux-pwm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-amlogic@...ts.infradead.org>,
        <linux-rockchip@...ts.infradead.org>,
        <linux-rpi-kernel@...ts.infradead.org>,
        <devicetree@...r.kernel.org>
Subject: Re: [PATCH v2 11/16] pwm: add documentation for PWM modes



On 20.01.2018 00:39, Rob Herring wrote:
> On Fri, Jan 12, 2018 at 04:22:58PM +0200, Claudiu Beznea wrote:
>> Add documentation for PWM normal and complementary modes.
> 
> This and the previous patch can be combined.
OK
> 
>>
>> Signed-off-by: Claudiu Beznea <claudiu.beznea@...rochip.com>
>> ---
>>  Documentation/devicetree/bindings/pwm/pwm.txt | 17 ++++++++++++++--
>>  Documentation/pwm.txt                         | 29 +++++++++++++++++++++++++--
>>  2 files changed, 42 insertions(+), 4 deletions(-)
>>
>> diff --git a/Documentation/devicetree/bindings/pwm/pwm.txt b/Documentation/devicetree/bindings/pwm/pwm.txt
>> index 8556263b8502..fdff25bad1db 100644
>> --- a/Documentation/devicetree/bindings/pwm/pwm.txt
>> +++ b/Documentation/devicetree/bindings/pwm/pwm.txt
>> @@ -43,8 +43,8 @@ because the name "backlight" would be used as fallback anyway.
>>  pwm-specifier typically encodes the chip-relative PWM number and the PWM
>>  period in nanoseconds.
>>  
>> -Optionally, the pwm-specifier can encode a number of flags (defined in
>> -<dt-bindings/pwm/pwm.h>) in a third cell:
>> +Optionally, the pwm-specifier can encode:
>> +1. a number of flags (defined in <dt-bindings/pwm/pwm.h>) in a third cell:
> 
> Based on the prior patches, "third cell" is probably to restrictive 
> here and it should just say "in a flags cell".
OK

Thank you,
Claudiu Beznea
> 
>>  - PWM_POLARITY_INVERTED: invert the PWM signal polarity
>>  
>>  Example with optional PWM specifier for inverse polarity
>> @@ -54,6 +54,19 @@ Example with optional PWM specifier for inverse polarity
>>  		pwm-names = "backlight";
>>  	};
>>  
>> +2. PWM working modes (defined in <dt-bindings/pwm/pwm.h>) in the 4th cell:
>> +- PWM_MODE_NORMAL: for all PWM controllers
>> +- PWM_MODE_COMPLEMENTARY: for PWM controllers with more than one output per
>> +PWM channel
>> +
>> +Example with PWM modes:
>> +
>> +	bl: blacklight {
>> +		pwms = <&pwm 0 5000000 PWM_POLARITY_INVERTED
>> +			PWM_DTMODE_NORMAL | PWM_DTMODE_COMPLEMENTARY>;
>> +		pwm-names = "backlight";
>> +	};
>> +
>>  2) PWM controller nodes
>>  -----------------------
>>  
>> diff --git a/Documentation/pwm.txt b/Documentation/pwm.txt
>> index 8fbf0aa3ba2d..58c9bd55f021 100644
>> --- a/Documentation/pwm.txt
>> +++ b/Documentation/pwm.txt
>> @@ -61,8 +61,8 @@ In addition to the PWM state, the PWM API also exposes PWM arguments, which
>>  are the reference PWM config one should use on this PWM.
>>  PWM arguments are usually platform-specific and allows the PWM user to only
>>  care about dutycycle relatively to the full period (like, duty = 50% of the
>> -period). struct pwm_args contains 2 fields (period and polarity) and should
>> -be used to set the initial PWM config (usually done in the probe function
>> +period). struct pwm_args contains 3 fields (period, polarity and mode) and
>> +should be used to set the initial PWM config (usually done in the probe function
>>  of the PWM user). PWM arguments are retrieved with pwm_get_args().
>>  
>>  Using PWMs with the sysfs interface
>> @@ -83,6 +83,9 @@ will find:
>>    unexport
>>     Unexports a PWM channel from sysfs (write-only).
>>  
>> +  mode
>> +   PWM chip supported modes.
>> +
>>  The PWM channels are numbered using a per-chip index from 0 to npwm-1.
>>  
>>  When a PWM channel is exported a pwmX directory will be created in the
>> @@ -110,6 +113,28 @@ channel that was exported. The following properties will then be available:
>>  	- 0 - disabled
>>  	- 1 - enabled
>>  
>> +  mode
>> +    Set PWM channel working mode (normal and complementary). PWM chip with
>> +    complementary mode could also work in normal mode by using only one physical
>> +    output.
>> +
>> +    Normal mode - for PWM chips with one output per PWM channel; output
>> +        waveforms looks like this:
>> +             __    __    __    __
>> +    PWM   __|  |__|  |__|  |__|  |__
>> +            <--T-->
>> +
>> +    Complementary mode - for PWM chips with more than one output per PWM
>> +        channel; output waveforms for a PWM controller with 2 outputs per PWM
>> +        channel looks line this:
>> +             __    __    __    __
>> +    PWMH1 __|  |__|  |__|  |__|  |__
>> +          __    __    __    __    __
>> +    PWML1   |__|  |__|  |__|  |__|
>> +            <--T-->
>> +
>> +    Where T is the signal period.
>> +
>>  Implementing a PWM driver
>>  -------------------------
>>  
>> -- 
>> 2.7.4
>>
>