linux-kernel - Re: [PATCH v5 3/3] leds: Add control of the voltage/current regulator to the LED core

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Date:   Mon, 14 Oct 2019 12:49:07 +0200
From:   Jean-Jacques Hiblot <jjhiblot@...com>
To:     Pavel Machek <pavel@....cz>,
        Jacek Anaszewski <jacek.anaszewski@...il.com>
CC:     <daniel.thompson@...aro.org>, <linux-leds@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <dmurphy@...com>,
        <tomi.valkeinen@...com>
Subject: Re: [PATCH v5 3/3] leds: Add control of the voltage/current regulator
 to the LED core


On 13/10/2019 14:09, Pavel Machek wrote:
> Hi!
>
>> I must say I'm not a big fan of this change.
>> It adds a bunch of code to the LED core and gives small
>> functionality in a reward. It may also influence maximum
>> software blinking rate, so I'd rather avoid calling
>> regulator_enable/disable when timer trigger is set.
>>
>> It will of course require more code.
>>
>> Since AFAIR Pavel was original proponent of this change then
>> I'd like to see his opinion before we move on to discussing
>> possible improvements to this patch.
> Was I?
>
> Okay, this series looks quite confusing to me. First, 1/3 looks
> "interesting" (would have to analyze it way more).
>
> Second, 3/3... So we have a LED driver _and_ a regulator? So yes, the
> chip driving a LED is usually ... voltage/current regulator. What is
> second regulator doing there? Is that a common setup?

This is quite common with current-sink LED drivers.

The setup looks like this:

+-----------+
|           |
| Regulator |
|           +------------------------+
|           |                        |
+-----------+                      __|__
                                    \   /
          +---------------------+    \ / led
          |                     |     V
          |    Led Driver       |   --+--
          |                     |     |
          |                     |     |
          |                +----------+
          |              \      |
          |               \     |
          |                +    |
          |                |    |
          +---------------------+
                           |
                        +--+--+
                        ///////


Only the regulator usually does not supply only one LED.

JJ


>
> Best regards,
> 								Pavel
>