Re: [PATCHv4 3/3] devicetree: Add led-backlight binding

[Tomi Valkeinen <tomi.valkeinen@ti.com>]

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Hi Rob,

On 13/10/15 17:21, Rob Herring wrote:
> On Wed, Sep 30, 2015 at 4:32 AM, Tomi Valkeinen <tomi.valkeinen@ti.com> wrote:
>> Add DT binding for led-backlight.
> 
> Please use get_maintainers.pl.

At some point I got feedback that the DT maintainers don't have time to
look at each individual driver binding, but rely on the subsystem
maintainers to handle them. Maybe I misunderstood that.

>> Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
>> Cc: devicetree@vger.kernel.org
>> ---
>>  .../bindings/video/backlight/led-backlight.txt     | 30 ++++++++++++++++++++++
>>  1 file changed, 30 insertions(+)
>>  create mode 100644 Documentation/devicetree/bindings/video/backlight/led-backlight.txt
>>
>> diff --git a/Documentation/devicetree/bindings/video/backlight/led-backlight.txt b/Documentation/devicetree/bindings/video/backlight/led-backlight.txt
>> new file mode 100644
>> index 000000000000..d4621d7414bc
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/video/backlight/led-backlight.txt
>> @@ -0,0 +1,30 @@
>> +led-backlight bindings
>> +
>> +Required properties:
>> +  - compatible: "led-backlight"
>> +  - leds: phandle to a led OF node [0]
> 
> Why do we need 2 levels of LED nodes?

Sorry, didn't get that. What do you mean with 2 levels?

>> +  - brightness-levels: Array of distinct LED brightness levels. These
>> +      are in the range from 0 to 255, passed to the LED class driver.
>> +  - default-brightness-level: the default brightness level (index into the
>> +      array defined by the "brightness-levels" property)
>> +
>> +Optional properties:
>> +  - power-supply: regulator for supply voltage
>> +  - enable-gpios: contains a single GPIO specifier for the GPIO which enables
>> +                  and disables the backlight (see GPIO binding[1])
> 
> Why are all of these not part of the LED node pointed to by leds?

These are for the backlight, not for the LED chip. So "LED" here is a
chip that produces (most likely) a PWM signal, and "backlight" is the
collection of components that use the PWM to produce the backlight
itself, and use the power-supply and gpios.

> Describe the h/w, not what you want for a driver.

I think this describes the HW quite well. The LED chip works fine
without any of the properties here, and these are specific to the
backlight part of the board.

 Tomi


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