linux-kernel - LED backlight on Droid 4 and others

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Message-ID: <20200105183202.GA17784@duo.ucw.cz>
Date:   Sun, 5 Jan 2020 19:32:02 +0100
From:   Pavel Machek <pavel@....cz>
To:     kernel list <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-omap@...r.kernel.org, tony@...mide.com, sre@...nel.org,
        nekit1000@...il.com, mpartap@....net, merlijn@...zup.org,
        martin_rysavy@...trum.cz, agx@...xcpu.org, lee.jones@...aro.org,
        daniel.thompson@...aro.org, jingoohan1@...il.com,
        dri-devel@...ts.freedesktop.org
Cc:     tomi.valkeinen@...com, jjhiblot@...com, daniel.thompson@...aro.org
Subject: LED backlight on Droid 4 and others

Hi!

It would be good to get LED backlight to work in clean way for 5.6
kernel.

As far as I can see, these are neccessary (but not enough; it does not
work for me): lm3532 changes to register LED with of node, plus device
tree changes for droid 4, and these generic changes:

commit d457d0c97d6d55fe3e62633791ac05d289a37d2e
Author: Tomi Valkeinen <tomi.valkeinen@...com>
Date:   Thu Oct 3 10:28:12 2019 +0200

    backlight: add led-backlight driver
    
    This patch adds a led-backlight driver (led_bl), which is similar to
    pwm_bl except the driver uses a LED class driver to adjust the
    brightness in the HW. Multiple LEDs can be used for a single backlight.
    
    Signed-off-by: Tomi Valkeinen <tomi.valkeinen@...com>
    Signed-off-by: Jean-Jacques Hiblot <jjhiblot@...com>
    Acked-by: Pavel Machek <pavel@....cz>
    Reviewed-by: Daniel Thompson <daniel.thompson@...aro.org>

commit 44b7adbf0b07904e4198ae1d0a763917d1c68a23
Author: Jean-Jacques Hiblot <jjhiblot@...com>
Date:   Thu Oct 3 10:28:10 2019 +0200

    leds: Add managed API to get a LED from a device driver
    
    If the LED is acquired by a consumer device with devm_led_get(), it is
    automatically released when the device is detached.
    
    Signed-off-by: Jean-Jacques Hiblot <jjhiblot@...com>
    Acked-by: Pavel Machek <pavel@....cz>
    Signed-off-by: Pavel <pavel@....cz>

commit 93b98c570d7f898063ab6204e1b3950a3335dd12
Author: Tomi Valkeinen <tomi.valkeinen@...com>
Date:   Thu Oct 3 10:28:09 2019 +0200

    leds: Add of_led_get() and led_put()
    
    This patch adds basic support for a kernel driver to get a LED device.
    This will be used by the led-backlight driver.
    
    Only OF version is implemented for now, and the behavior is similar to
    PWM's of_pwm_get() and pwm_put().
    
    Signed-off-by: Tomi Valkeinen <tomi.valkeinen@...com>
    Signed-off-by: Jean-Jacques Hiblot <jjhiblot@...com>
    Acked-by: Pavel Machek <pavel@....cz>
    Signed-off-by: Pavel <pavel@....cz>

[If you have an idea what else is needed, it would be welcome; it
works for me in development tree but not in tree I'd like to
upstream.]

Lee, would you be willing to take "backlight: add led-backlight
driver"? Would it help if I got "leds: Add managed API to get a LED
from a device driver" and "leds: Add of_led_get() and led_put()" into
for_next tree of the LED subsystem?

It is kind of important as, well, phone without screen looks pretty
much dead, and same issue hits Droid 4 and Librem 5 phones at least...

Best regards,
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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