linux-kernel - Re: [PATCH 3/4] backlight: add led-backlight driver

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Message-ID: <6c21af33-8c3b-58a8-0a1b-f85fb9f80050@ti.com>
Date:   Fri, 5 Jul 2019 12:33:33 +0200
From:   Jean-Jacques Hiblot <jjhiblot@...com>
To:     Pavel Machek <pavel@....cz>
CC:     Daniel Thompson <daniel.thompson@...aro.org>,
        <jacek.anaszewski@...il.com>, <robh+dt@...nel.org>,
        <mark.rutland@....com>, <lee.jones@...aro.org>,
        <jingoohan1@...il.com>, <dmurphy@...com>,
        <linux-leds@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <dri-devel@...ts.freedesktop.org>, <tomi.valkeinen@...com>
Subject: Re: [PATCH 3/4] backlight: add led-backlight driver

Pavel

On 05/07/2019 12:08, Pavel Machek wrote:
> Hi!
>
>>>>> Also still relevant is whether the LED device is being correctly
>>>>> modelled if the act of turning on the LED doesn't, in fact, turn the LED
>>>>> on. Is it *really* a correct implementation of an LED device that
>>>>> setting it to LED_FULL using sysfs doesn't cause it to light up?
>>>> What I understood from the discussion between Rob and Tomi is that the
>>>> child-node of the LED controller should be considered a backlight device,
>>>> not a simple LED. I'm not sure if the sysfs interface is still relevant in
>>>> that case. Maybe it should just be disabled by the backlight driver
>>>> (possible with led_sysfs_disable())
>>> led_sysfs_disable() sounds like a sensible change but that's not quite
>>> what I mean.
>>>
>>> It is more a thought experiment to see if the power control *should* be
>>> implemented by the backlight. Consider what happens if we *don't*
>>> enable CONFIG_BACKLIGHT_LED in the kernel: we would still have an LED
>>> device and it would not work correctly.
>>>
>>> In other words I naively expect turning on an LED using the LED API
>>> (any of them, sysfs or kernel) to result in the LED turning on.
>>> Implementing a workaround in the client for what appears to be
>>> something missing in the LED driver strikes me as odd. Why shouldn't
>>> the regulator be managed in the LED driver?
>> I see your point. Indeed having the regulator handled in the LED-core makes
>> sense in a lot of situations
>>
>> I'll think about it.
> For the record, I also believe regulator and enable gpio should be
> handled in the core.

I am working on adding the regulator to the led core.

I don't really want to add a GPIO enable to the core though. If needed 
it can be described as a GPIO-enabled regulator up(/down)stream the 
regular regulator.

JJ


>
> 									Pavel
> PS please trim down the quoted text.