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Date:   Mon, 14 Oct 2019 13:38:49 +0100
From:   Daniel Thompson <daniel.thompson@linaro.org>
To:     Jean-Jacques Hiblot <jjhiblot@ti.com>
Cc:     Pavel Machek <pavel@ucw.cz>,
        Jacek Anaszewski <jacek.anaszewski@gmail.com>,
        linux-leds@vger.kernel.org, linux-kernel@vger.kernel.org,
        dmurphy@ti.com, tomi.valkeinen@ti.com
Subject: Re: [PATCH v5 3/3] leds: Add control of the voltage/current
 regulator to the LED core
Message-ID: <20191014123849.fhvmqn7dyu6bminc@holly.lan>
References: <20190923102059.17818-1-jjhiblot@ti.com>
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 <3e648fab-638f-4aa0-dda9-8ddba6562751@gmail.com>
 <20191013120937.GK5653@amd>
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On Mon, Oct 14, 2019 at 12:49:07PM +0200, Jean-Jacques Hiblot wrote:
> 
> 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.

Given questions have been raised about the complexity of the change I
wondered whether, for a system with this topology, the regulator
could/should be enabled when the LED driver driver probes?


Daniel.