linux-kernel - Re: [PATCH 2/2] dt-bindings: leds: document new "power-supply" property

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Message-ID: <753b2c8d-e8fc-ec6e-f372-a84d4452fd33@ti.com>
Date:   Thu, 25 Jul 2019 13:08:46 +0200
From:   Jean-Jacques Hiblot <jjhiblot@...com>
To:     Rob Herring <robh@...nel.org>
CC:     <jacek.anaszewski@...il.com>, <pavel@....cz>,
        <mark.rutland@....com>, <daniel.thompson@...aro.org>,
        <dmurphy@...com>, <linux-leds@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <devicetree@...r.kernel.org>
Subject: Re: [PATCH 2/2] dt-bindings: leds: document new "power-supply"
 property

Hi Rob,

On 24/07/2019 18:47, Rob Herring wrote:
> On Mon, Jul 08, 2019 at 12:35:47PM +0200, Jean-Jacques Hiblot wrote:
>> Most of the LEDs are powered by a voltage/current regulator. describing in
>> the device-tree makes it possible for the LED core to enable/disable it
>> when needed.
>>
>> Signed-off-by: Jean-Jacques Hiblot <jjhiblot@...com>
>> ---
>>   Documentation/devicetree/bindings/leds/common.txt | 5 +++++
>>   1 file changed, 5 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/leds/common.txt b/Documentation/devicetree/bindings/leds/common.txt
>> index 70876ac11367..e093a2b7eb90 100644
>> --- a/Documentation/devicetree/bindings/leds/common.txt
>> +++ b/Documentation/devicetree/bindings/leds/common.txt
>> @@ -61,6 +61,11 @@ Optional properties for child nodes:
>>   - panic-indicator : This property specifies that the LED should be used,
>>   		    if at all possible, as a panic indicator.
>>   
>> +- power-supply : A voltage/current regulator used to to power the LED. When a
>> +		 LED is turned off, the LED core disable its regulator. The
>> +		 same regulator can power many LED (or other) devices. It is
>> +		 turned off only when all of its users disabled it.
> Not sure this should be common. It wouldn't apply to cases where we have
> an LED controller parent nor gpio and pwm LEDs and those are most cases.

It does make sense for GPIO and PWM bindings if the anode of LED is tied 
to a regulated voltage and the cathod to the control line.

The same is true for a certain class of true LED controller that do not 
deliver power but act like current sinks.

JJ

>
> Perhaps what makes sense here is an regulator-led binding.
>
>> +
>>   - trigger-sources : List of devices which should be used as a source triggering
>>   		    this LED activity. Some LEDs can be related to a specific
>>   		    device and should somehow indicate its state. E.g. USB 2.0
>> -- 
>> 2.17.1
>>