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

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Message-ID: <20180119223908.b3dxdx53nzuhakzw@rob-hp-laptop>
Date:   Fri, 19 Jan 2018 16:39:08 -0600
From:   Rob Herring <robh@...nel.org>
To:     Claudiu Beznea <claudiu.beznea@...rochip.com>
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 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.

> 
> 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".

>  - 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
>