linux-kernel - Re: [PATCH] leds: leds-gpio: Add a condition check for active low leds.

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Message-ID: <20180905095254.GA9579@amd>
Date:   Wed, 5 Sep 2018 11:52:54 +0200
From:   Pavel Machek <pavel@....cz>
To:     Michal Vokáč <michal.vokac@...ft.com>
Cc:     Song Qiang <songqiang1304521@...il.com>,
        jacek.anaszewski@...il.com, robh+dt@...nel.org,
        mark.rutland@....com, linux-leds@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Song Qiang <songqiang.1304521@...il.com>
Subject: Re: [PATCH] leds: leds-gpio: Add a condition check for active low
 leds.

On Wed 2018-09-05 09:44:04, Michal Vokáč wrote:
> Hi Song,
> On 5.9.2018 04:34, Song Qiang wrote:
> >Some leds on our board are active low leds, which means these leds
> >are lighted when the corresponding gpio line is low, while the
> >original leds-gpio driver default all leds are active high leds.
> >This patch adds a devicetree node "light-state", whose value should
> >be "high" for active high leds and "low" for active low leds.
> >The default value is "high" for compatible for the original driver.
> >
> >Signed-off-by: Song Qiang <songqiang.1304521@...il.com>
> >---
> >  .../devicetree/bindings/leds/leds-gpio.txt    | 15 +++++++++++
> >  drivers/leds/leds-gpio.c                      | 25 +++++++++++++++++--
> >  2 files changed, 38 insertions(+), 2 deletions(-)
> >
> >diff --git a/Documentation/devicetree/bindings/leds/leds-gpio.txt b/Documentation/devicetree/bindings/leds/leds-gpio.txt
> >index a48dda268f81..0a8fad75c704 100644
> >--- a/Documentation/devicetree/bindings/leds/leds-gpio.txt
> >+++ b/Documentation/devicetree/bindings/leds/leds-gpio.txt
> >@@ -23,6 +23,9 @@ LED sub-node properties:
> >    remains up.
> >  - panic-indicator : (optional)
> >    see Documentation/devicetree/bindings/leds/common.txt
> >+- light-state: (optional) Values should be "high" or "low", which indicates
> >+	the state of the GPIO pin when the led is on.
> >+  see Documentation/devicetree/bindings/leds/common.txt
> >  Examples:
> >@@ -64,3 +67,15 @@ leds {
> >  		retain-state-suspended;
> >  	};
> >  };
> >+
> >+leds {
> >+	compatible = "gpio-leds";
> >+
> >+	led0 {
> >+		label = "led0";
> >+		gpios = <&gpio1 19 GPIO_ACTIVE_HIGH>;
> 
> With this patch you are introducing one more way to invert the logic.
> If your LED is active LOW, you should use GPIO_ACTIVE_LOW in your DT.
> All should work as expected then.

Exactly, GPIO subsystem already has ways to specify active-low and
active-high.

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

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