linux-kernel - Re: [PATCH v3 3/4] dt-bindings: backlight: Add led-backlight binding

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Message-ID: <0d513ab5-eeb0-c22c-7ec8-f773e445e5f1@ti.com>
Date:   Fri, 12 Jul 2019 15:57:20 +0200
From:   Jean-Jacques Hiblot <jjhiblot@...com>
To:     Pavel Machek <pavel@....cz>
CC:     <jacek.anaszewski@...il.com>, <robh+dt@...nel.org>,
        <mark.rutland@....com>, <lee.jones@...aro.org>,
        <daniel.thompson@...aro.org>, <jingoohan1@...il.com>,
        <dmurphy@...com>, <linux-leds@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
        <tomi.valkeinen@...com>
Subject: Re: [PATCH v3 3/4] dt-bindings: backlight: Add led-backlight binding

Pavel,

On 10/07/2019 21:13, Pavel Machek wrote:
> On Wed 2019-07-10 14:39:31, Jean-Jacques Hiblot wrote:
>> Add DT binding for led-backlight.
>>
>> Signed-off-by: Jean-Jacques Hiblot <jjhiblot@...com>
>> ---
>>   .../bindings/leds/backlight/led-backlight.txt | 28 +++++++++++++++++++
>>   1 file changed, 28 insertions(+)
>>   create mode 100644 Documentation/devicetree/bindings/leds/backlight/led-backlight.txt
>>
>> diff --git a/Documentation/devicetree/bindings/leds/backlight/led-backlight.txt b/Documentation/devicetree/bindings/leds/backlight/led-backlight.txt
>> new file mode 100644
>> index 000000000000..0444eec8efe1
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/leds/backlight/led-backlight.txt
>> @@ -0,0 +1,28 @@
>> +led-backlight bindings
>> +
>> +This binding is used to describe a basic backlight device made of
>> LEDs.
> Ok.
>
>> +It can also be used to describe a backlight device controlled by the output of
>> +a LED driver.
> ? The LED driver should better be driving some LEDs...

Well. we are dependent of the board design. If a board designer decided 
to control a backlight with a LED-controller, then we have to deal with it.

In practice there are a lot of LED drivers that actually drive the LEDs 
using PWMs and can be used for this purpose.

JJ

>
>> +Required properties:
>> +  - compatible: "led-backlight"
>> +  - leds: a list of LEDs
>> +
>> +Optional properties:
>> +  - brightness-levels: Array of distinct brightness levels. The levels must be
>> +                       in the range accepted by the underlying LED devices.
>> +                       This is used to translate a backlight brightness level
>> +                       into a LED brightness level. if not provided, the
>> +                       identity mapping is used.
> "If it is not"
> 									Pavel