linux-kernel - Re: [PATCH 2/2] dt-bindings: leds: document new "power-supply" property

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Message-ID: <20190726100607.j5bdmuuk33zpwa2r@holly.lan>
Date:   Fri, 26 Jul 2019 11:06:07 +0100
From:   Daniel Thompson <daniel.thompson@...aro.org>
To:     Jean-Jacques Hiblot <jjhiblot@...com>
Cc:     Rob Herring <robh@...nel.org>, jacek.anaszewski@...il.com,
        pavel@....cz, mark.rutland@....com, dmurphy@...com,
        linux-leds@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH 2/2] dt-bindings: leds: document new "power-supply"
 property

On Thu, Jul 25, 2019 at 01:08:46PM +0200, Jean-Jacques Hiblot wrote:
> Hi Rob,
> 
> On 24/07/2019 18:47, Rob Herring wrote:
> > On Mon, Jul 08, 2019 at 12:35:47PM +0200, Jean-Jacques Hiblot wrote:
> > > Most of the LEDs are powered by a voltage/current regulator. describing in
> > > the device-tree makes it possible for the LED core to enable/disable it
> > > when needed.
> > > 
> > > Signed-off-by: Jean-Jacques Hiblot <jjhiblot@...com>
> > > ---
> > >   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 70876ac11367..e093a2b7eb90 100644
> > > --- a/Documentation/devicetree/bindings/leds/common.txt
> > > +++ b/Documentation/devicetree/bindings/leds/common.txt
> > > @@ -61,6 +61,11 @@ Optional properties for child nodes:
> > >   - panic-indicator : This property specifies that the LED should be used,
> > >   		    if at all possible, as a panic indicator.
> > > +- power-supply : A voltage/current regulator used to to power the LED. When a
> > > +		 LED is turned off, the LED core disable its regulator. The
> > > +		 same regulator can power many LED (or other) devices. It is
> > > +		 turned off only when all of its users disabled it.
> > Not sure this should be common. It wouldn't apply to cases where we have
> > an LED controller parent nor gpio and pwm LEDs and those are most cases.
> 
> It does make sense for GPIO and PWM bindings if the anode of LED is tied to
> a regulated voltage and the cathod to the control line.
> 
> The same is true for a certain class of true LED controller that do not
> deliver power but act like current sinks.
> 
> JJ
> 
> > 
> > Perhaps what makes sense here is an regulator-led binding.

You didn't comment on this alternative... and I confess I'm not quite
sure what Rob means by a regulator-led binding so I can't really comment
either.

Rob, is there any analogous example for a regulator-<something-else> binding
to compare with?


Daniel.

> > 
> > > +
> > >   - trigger-sources : List of devices which should be used as a source triggering
> > >   		    this LED activity. Some LEDs can be related to a specific
> > >   		    device and should somehow indicate its state. E.g. USB 2.0
> > > -- 
> > > 2.17.1
> > >