linux-kernel - Re: [PATCH/RFC v10 03/19] DT: leds: Add led-sources property

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Date:	Mon, 12 Jan 2015 10:55:29 -0600
From:	Rob Herring <robherring2@...il.com>
To:	Jacek Anaszewski <j.anaszewski@...sung.com>
Cc:	linux-leds@...r.kernel.org,
	"linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Pavel Machek <pavel@....cz>, Bryan Wu <cooloney@...il.com>,
	Richard Purdie <rpurdie@...ys.net>, sakari.ailus@....fi,
	Sylwester Nawrocki <s.nawrocki@...sung.com>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Liam Girdwood <lgirdwood@...il.com>,
	Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH/RFC v10 03/19] DT: leds: Add led-sources property

Adding Mark B and Liam...

On Mon, Jan 12, 2015 at 10:10 AM, Jacek Anaszewski
<j.anaszewski@...sung.com> wrote:
> On 01/12/2015 02:52 PM, Rob Herring wrote:
>>
>> On Mon, Jan 12, 2015 at 2:32 AM, Jacek Anaszewski
>> <j.anaszewski@...sung.com> wrote:
>>> On 01/09/2015 07:33 PM, Rob Herring wrote:
>>>> On Fri, Jan 9, 2015 at 9:22 AM, Jacek Anaszewski
>>>> <j.anaszewski@...sung.com> wrote:
>>>>> Add a property for defining the device outputs the LED
>>>>> represented by the DT child node is connected to.

[...]

>>>>> b/Documentation/devicetree/bindings/leds/common.txt
>>>>> index a2c3f7a..29295bf 100644
>>>>> --- a/Documentation/devicetree/bindings/leds/common.txt
>>>>> +++ b/Documentation/devicetree/bindings/leds/common.txt
>>>>> @@ -1,6 +1,10 @@
>>>>>    Common leds properties.
>>>>>
>>>>>    Optional properties for child nodes:
>>>>> +- led-sources : Array of bits signifying the LED current regulator
>>>>> outputs the
>>>>> +               LED represented by the child node is connected to (1 -
>>>>> the LED
>>>>> +               is connected to the output, 0 - the LED isn't connected
>>>>> to the
>>>>> +               output).
>>>>
>>>>
>>>>
>>>> Sorry, I just don't understand this.
>>>
>>>
>>>
>>> In some Flash LED devices one LED can be connected to one or more
>>> electric current outputs, which allows for multiplying the maximum
>>> current allowed for the LED. Each sub-LED is represented by a child
>>> node in the DT binding of the Flash LED device and it needs to declare
>>> which outputs it is connected to. In the example below the led-sources
>>> property is a two element array, which means that the flash LED device
>>> has two current outputs, and the bits signify if the LED is connected
>>> to the output.
>>
>>
>> Sounds like a regulator for which we already have bindings for and we
>> have a driver for regulator based LEDs (but no binding for it).
>
>
> Do you think of drivers/leds/leds-regulator.c driver? This driver just
> allows for registering an arbitrary regulator device as a LED subsystem
> device.
>
> There are however devices that don't fall into this category, i.e. they
> have many outputs, that can be connected to a single LED or to many LEDs
> and the driver has to know what is the actual arrangement.

We may need to extend the regulator binding slightly and allow for
multiple phandles on a supply property, but wouldn't something like
this work:

led-supply = <&led-reg0>, <&led-reg1>, <&led-reg2>, <&led-reg3>;

The shared source is already supported by the regulator binding.

Rob

>
>> Please use the regulator binding.
>
>
>>> Do your doubts stem from the ambiguity of the word "current" or the
>>> form of the description itself is unclear? Probably there should be
>>> explicit explanation added that the size of the array depends on the
>>> number of current outputs of the flash LED device.
>>
>>
>> The size of the array and meaning of array indexes was not clear.
>
>
> What about this:
>
> led-sources : Array of connection states between all LED current
>               sources exposed by the device and this LED (1 - this LED
>               is connected to the current output with index N, 0 -
>               this LED isn't connected to the current output with
>               index N); the mapping of N-th element of the array to the
>               physical device output should be defined in the LED
>               driver binding.
>
>
> --
> Best Regards,
> Jacek Anaszewski
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