linux-kernel - Re: [PATCH v1 2/2] dt: bindings: lp50xx: Add max-brightness as in leds-pwm

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Date:   Fri, 30 Jun 2023 09:23:33 +0200
From:   Astrid Rost <astridr@...s.com>
To:     Rob Herring <robh@...nel.org>, Astrid Rost <astrid.rost@...s.com>
CC:     Dan Murphy <dmurphy@...com>, Andrew Davis <afd@...com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Pavel Machek <pavel@....cz>, Lee Jones <lee@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>, <kernel@...s.com>,
        <linux-leds@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 2/2] dt: bindings: lp50xx: Add max-brightness as in
 leds-pwm



On 6/29/23 19:59, Rob Herring wrote:
> On Thu, Jun 29, 2023 at 03:47:22PM +0200, Astrid Rost wrote:
>> Add max-brightness in order to reduce the current on the connected LEDs.
>> Normally, the maximum brightness is determined by the hardware, and this
>> property is not required. This property is used to set a software limit.
>> It could happen that an LED is made so bright that it gets damaged or
>> causes damage due to restrictions in a specific system, such as mounting
>> conditions.
>>
>> Signed-off-by: Astrid Rost <astrid.rost@...s.com>
>> ---
>>   Documentation/devicetree/bindings/leds/leds-lp50xx.yaml | 9 +++++++++
>>   1 file changed, 9 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/leds/leds-lp50xx.yaml b/Documentation/devicetree/bindings/leds/leds-lp50xx.yaml
>> index 402c25424525..6a1425969cb4 100644
>> --- a/Documentation/devicetree/bindings/leds/leds-lp50xx.yaml
>> +++ b/Documentation/devicetree/bindings/leds/leds-lp50xx.yaml
>> @@ -73,6 +73,15 @@ patternProperties:
>>         '#size-cells':
>>           const: 0
>>   
>> +      max-brightness:
>> +        description:
>> +          Normally, the maximum brightness is determined by the hardware, and
>> +          this property is not required. This property is used to set a software
>> +          limit. It could happen that an LED is made so bright that it gets
>> +          damaged or causes damage due to restrictions in a specific system,
>> +          such as mounting conditions.
>> +        $ref: /schemas/types.yaml#definitions/uint32
> 
> We already have led-max-microamp. If this h/w works by controlling the
> current, then that is what you should use. "max-brightness" makes more
> sense for PWM based control.

Yes, I looked into this. This LED controller TI-LP5024 has only one flag 
as max current option, which allows to set between 35 mA and the default 
value 25.5 mA. This is not enough for our application.

> 
> If you do end up keeping this, it belongs in the 'led' nodes not the
> controller as brightness is a property of the LED, not the LED
> driver(controller). And it should be in common schema rather than
> defining the type yet again.

I will look moving it into the the LED generic bindings as Andy 
suggested. max_brightness is already there and handled correctly. It is 
just a matter of reading it from the devicetree.

> 
> Rob