linux-kernel - Re: [PATCH v2 1/2] leds: ncp5623: Add device tree binding documentation

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Message-id: <5770E4EB.4040609@samsung.com>
Date:	Mon, 27 Jun 2016 10:33:47 +0200
From:	Jacek Anaszewski <j.anaszewski@...sung.com>
To:	Florian Vaussard <florian.vaussard@...g-vd.ch>
Cc:	Florian Vaussard <florian.vaussard@...il.com>,
	devicetree@...r.kernel.org, Richard Purdie <rpurdie@...ys.net>,
	Rob Herring <robh+dt@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Pavel Machek <pavel@....cz>, linux-leds@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] leds: ncp5623: Add device tree binding documentation

On 06/27/2016 10:30 AM, Florian Vaussard wrote:
> Hi Jacek,
>
> Le 27. 06. 16 à 10:11, Jacek Anaszewski a écrit :
>> Hi Florian,
>>
>> On 06/27/2016 09:03 AM, Florian Vaussard wrote:
>>> Add device tree binding documentation for On Semiconductor NCP5623 I2C
>>> LED driver. The driver can independently control the PWM of the 3
>>> channels with 32 levels of intensity.
>>>
>>> The current delivered by the current source can also be controlled. To
>>> do so, the led-max-microamp property is used by each LED sub-node. The
>>> maximum value is then found and used as a limit to compute the final
>>> intensity of the current source. If a LED happens to have a lower limit,
>>> the PWM is then used to limit the current to the requested value.
>>>
>>> In order to control the current source, it is also necessary to know
>>> the current on the Iref pin, hence the onnn,led-iref-microamp property.
>>> It is usually set using an external bias resistor, following
>>> Iref = Vref/Rbias with Vref=0.6V.
>>>
>>> Signed-off-by: Florian Vaussard <florian.vaussard@...g-vd.ch>
>>> ---
>>>    .../devicetree/bindings/leds/leds-ncp5623.txt      | 60 ++++++++++++++++++++++
>>>    1 file changed, 60 insertions(+)
>>>    create mode 100644 Documentation/devicetree/bindings/leds/leds-ncp5623.txt
>>>
>>> diff --git a/Documentation/devicetree/bindings/leds/leds-ncp5623.txt
>>> b/Documentation/devicetree/bindings/leds/leds-ncp5623.txt
>>> new file mode 100644
>>> index 0000000..77dd7ad
>>> --- /dev/null
>>> +++ b/Documentation/devicetree/bindings/leds/leds-ncp5623.txt
>>> @@ -0,0 +1,60 @@
>>> +* ON Semiconductor - NCP5623 3-Channel LED Driver
>>> +
>>> +The NCP5623 is a 3-channel I2C LED driver. The brightness of each
>>> +channel can be independently set using 32 levels. Each LED is represented
>>> +as a sub-node of the device.
>>> +
>>> +Required properties:
>>> +  - compatible: Should be "onnn,ncp5623"
>>> +  - reg: I2C slave address (fixed to 0x38)
>>> +  - #address-cells: must be 1
>>> +  - #size-cells: must be 0
>>> +  - onnn,led-iref-microamp: Current on the Iref pin in microampere. It depends
>>> +    on the value of the external bias resistor Rbias, following
>>> +    Iref = Vref / Rbias with Vref = 0.6V. This is used to set the intensity of
>>> +    the current that can be provided by the internal current source, based on
>>> +    the maximum current permitted by LED sub-nodes (see below), but no more than
>>> +    Imax = 2400 * Iref.
>>> +
>>> +LED sub-nodes
>>> +=============
>>> +
>>> +Required properties:
>>> +  - reg : LED channel number (0..2)
>>> +  - led-max-microamp: Maximum allowable current inside the LED in microampere.
>>> +    This property is used to limit the PWM ratio, based on the intensity of the
>>> +    internal current source (see above).
>>> +
>>> +Optional properties:
>>> +  - label: Used for naming LEDs
>>
>> Instead of the above description use same reference to common led
>> bindings as below.
>>
>
> Ok.
>
> BTW I saw the thread about the "default-state" property on the DT list and
> realized that it was not implemented in my driver. I wonder if standard LED
> properties (with label and default-trigger) should not be parsed by LED core
> (i.e. using a helper function) to avoid such mistake. This could also remove
> some boilerplate code in other LED drivers.

Yes, generic DT parser is a nice-to-have feature for the LED subsystem.
Would you like to implement it?

>
>>> +  - default-trigger: see Documentation/devicetree/bindings/leds/common.txt
>>> +
>>> +Example
>>> +=======
>>> +
>>> +led1: ncp5623@38 {
>>> +    #address-cells = <1>;
>>> +    #size-cells = <0>;
>>> +    compatible = "onnn,ncp5623";
>>> +    reg = <0x38>;
>>> +    onnn,led-iref-microamp = <10>;
>>> +
>>> +    led1r@0 {
>>> +        label = "ncp:power:red";
>>> +        linux,default-trigger = "default-on";
>>> +        reg = <0>;
>>> +        led-max-microamp = <20000>;
>>> +    };
>>> +
>>> +    led1b@1 {
>>> +        label = "ncp:power:blue";
>>> +        reg = <1>;
>>> +        led-max-microamp = <20000>;
>>> +    };
>>> +
>>> +    led1g@2 {
>>> +        label = "ncp:power:green";
>>> +        reg = <2>;
>>> +        led-max-microamp = <20000>;
>>> +    };
>>> +};
>>>
>>
>>
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>


-- 
Best regards,
Jacek Anaszewski