linux-kernel - Re: [PATCH 4/4] leds: lm3532: Introduce the lm3532 LED driver

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Message-ID: <20190403235500.GU49658@atomide.com>
Date:   Wed, 3 Apr 2019 16:55:00 -0700
From:   Tony Lindgren <tony@...mide.com>
To:     Sebastian Reichel <sre@...nel.org>
Cc:     Dan Murphy <dmurphy@...com>, robh+dt@...nel.org,
        jacek.anaszewski@...il.com, pavel@....cz, lee.jones@...aro.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-leds@...r.kernel.org
Subject: Re: [PATCH 4/4] leds: lm3532: Introduce the lm3532 LED driver

* Tony Lindgren <tony@...mide.com> [190403 13:06]:
> * Sebastian Reichel <sre@...nel.org> [190329 05:36]:
> > Hi,
> > 
> > On Mon, Mar 25, 2019 at 11:01:18AM -0500, Dan Murphy wrote:
> > > On 3/25/19 9:54 AM, Tony Lindgren wrote:
> > > > * Dan Murphy <dmurphy@...com> [190325 12:36]:
> > > >> On 3/22/19 5:16 PM, Tony Lindgren wrote:
> > > >>> I can control the backlight brightness just fine via /sys, and
> > > >>> backlight shows up as the trigger in /sys/class/leds/lm3532:backlight,
> > > >>> but /sys/class/backlight is empty and looks like drm can't find it.
> > > >>>
> > > >>> Do I need to enable some additional driver(s) to get this to work
> > > >>> with the drm driver?
> > > >>>
> > > >>
> > > >> Can you dump or point to the defconfig?
> > > > 
> > > > This is just with the omap2plus_defconfig as in the droid4-pending-v5.0
> > > > test branch below [0]. That branch has Sebastian's drm patches. The
> > > > branch also has the older ti-lmu patches that I reverted for testing
> > > > before applying your new series and enabling it in .config.
> > > > 
> > > > The drm driver (drivers/gpu/drm/omapdrm/displays/panel-dsi-cm.c) just
> > > > does:
> > > > 
> > > > backlight = of_parse_phandle(node, "backlight", 0);
> > > > ...
> > > > 
> > > > That should still work the same, right?
> > > 
> > > Yes it should still work the same.
> > > I did not change the node name.
> > > So the DRM driver should find the node.
> > 
> > This will not work, since the next line tries to get it as a
> > backlight device, but it's an LED device instead:
> > 
> > of_find_backlight_by_node(backlight);
> > 
> > I suppose the backlight device could be instantiated on top
> > of the LED device somehow.
> 
> Hmm yeah I thought setting the ledtrig-backlight for it
> would do the trick. But after thinking about it there might
> be some backlight lifecycle issues with that where everything
> would need to be torn down for the panel to change the
> backlight trigger. I think the panel driver(s) assume the
> backlight to always be there at probe time. Well this is
> just based on just guessing.. I might be wrong.
> 
> I have no issues using of_find_backlight_by_node() like
> other panels.

Oh sorry, I did not read the code before replying.
I somehow thought of_find_backlight_by_node() should be
used for LEDs but that's for backlight still :)

Looks like all we need to do is leave out the backlight
line from dts, we don't need to do anything with
of_find_backlight_by_node(). Having ledtrig-backlight
configured means lm3532 will just use the notifier
for FB_EVENT_BLANK.

I'll reply to the dts patch and ack the test, looks
like we're good to go as far as I'm concerned.

Regards,

Tony