From: Jean-Jacques Hiblot <jjhiblot@ti.com>
To: Jacek Anaszewski <jacek.anaszewski@gmail.com>,
Daniel Thompson <daniel.thompson@linaro.org>
Cc: Pavel Machek <pavel@ucw.cz>, <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
Date: Wed, 16 Oct 2019 10:13:54 +0200 [thread overview]
Message-ID: <5e4ad085-4091-2c43-4001-3378076fd455@ti.com> (raw)
In-Reply-To: <939cf695-b955-da01-2a2b-3b5ce0dc3660@gmail.com>
On 14/10/2019 20:48, Jacek Anaszewski wrote:
> On 10/14/19 2:38 PM, Daniel Thompson wrote:
>> 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?
> And this is how are doing that now.
>
> Moreover, just after seeing your ASCII art it has become obvious to me
> that we can't simply do regulator_disable() while setting brightness to
> LED_OFF since it can result in powering off the LED controller, which
> would need to be reconfigured on next transition to
> brightness > LED_OFF.
That is a problem only if the LED driver is powered by the same
regulator, which is not the case in the diagram.
This series make sense only for boards where LEDs have a dedicated
voltage rail or can be modeled this way.
My use case is a LED panel driven by a LED current-sink controller that
uses both a PWM-style control for brightness AND a active-low enable
pin. If the enable pin is not HIGH, the panel is never completely dark
even if the LED brightness is set to 0. I modeled this switch with a
fixed-voltage regulator which is a common way of doing it (it is after
all how this things is done inside the panel).
JJ
> It looks that the idea is flawed I'm afraid.
next prev parent reply other threads:[~2019-10-16 8:14 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-23 10:20 [PATCH v5 0/3] leds: Add control of the voltage/current regulator to the LED core Jean-Jacques Hiblot
2019-09-23 10:20 ` [PATCH v5 1/3] led: make led_set_brightness_sync() use led_set_brightness_nosleep() Jean-Jacques Hiblot
2019-09-23 10:20 ` [PATCH v5 2/3] dt-bindings: leds: document the "power-supply" property Jean-Jacques Hiblot
2019-09-23 10:20 ` [PATCH v5 3/3] leds: Add control of the voltage/current regulator to the LED core Jean-Jacques Hiblot
2019-09-24 18:58 ` Jacek Anaszewski
2019-09-25 8:41 ` Jean-Jacques Hiblot
2019-10-13 12:09 ` Pavel Machek
2019-10-13 16:40 ` Jacek Anaszewski
2019-10-14 10:49 ` Jean-Jacques Hiblot
2019-10-14 12:38 ` Daniel Thompson
2019-10-14 18:48 ` Jacek Anaszewski
2019-10-16 8:13 ` Jean-Jacques Hiblot [this message]
2019-10-17 19:05 ` Jacek Anaszewski
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