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

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Date:	Mon, 12 Jan 2015 17:10:23 +0100
From:	Jacek Anaszewski <j.anaszewski@...sung.com>
To:	Rob Herring <robherring2@...il.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>
Subject: Re: [PATCH/RFC v10 03/19] DT: leds: Add led-sources property

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.
>>>>
>>>> Signed-off-by: Jacek Anaszewski <j.anaszewski@...sung.com>
>>>> Acked-by: Kyungmin Park <kyungmin.park@...sung.com>
>>>> Cc: Bryan Wu <cooloney@...il.com>
>>>> Cc: Richard Purdie <rpurdie@...ys.net>
>>>> Cc: Rob Herring <robh+dt@...nel.org>
>>>> Cc: Pawel Moll <pawel.moll@....com>
>>>> Cc: Mark Rutland <mark.rutland@....com>
>>>> Cc: Ian Campbell <ijc+devicetree@...lion.org.uk>
>>>> Cc: Kumar Gala <galak@...eaurora.org>
>>>> ---
>>>>    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 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.

> 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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