linux-kernel - Re: [PATCH] backlight: led_bl: Add support for an "enable" GPIO

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Message-ID: <20211102112514.75v7evbdp4ccyyt5@maple.lan>
Date:   Tue, 2 Nov 2021 11:25:14 +0000
From:   Daniel Thompson <daniel.thompson@...aro.org>
To:     Corentin LABBE <clabbe@...libre.com>
Cc:     lee.jones@...aro.org, jingoohan1@...il.com,
        dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, khilman@...libre.com,
        Jean-Jacques Hiblot <jjhiblot@...com>,
        Pavel Machek <pavel@....cz>
Subject: Re: [PATCH] backlight: led_bl: Add support for an "enable" GPIO

On Tue, Nov 02, 2021 at 11:19:42AM +0000, Daniel Thompson wrote:
> On Tue, Nov 02, 2021 at 10:04:55AM +0000, Corentin LABBE wrote:
> > From: Jean-Jacques Hiblot <jjhiblot@...com>
> > 
> > This patch adds support for an "enable GPIO".
> 
> Before taking this kind of change is there a good reason why backlight
> should manage the GPIO? I thought that the LED subsystem was a sub
> system for LEDs (not LED controllers). In other words if you direct
> that the LED be lit up then isn't it the LED driver's job to manage
> the GPIO and ensure that it lights up?

Sorry... I should have paid more attention to my sense of déjà vu with
this patch.

This approach was discussed and rejected when we first introduced the
led_bl driver:
https://lore.kernel.org/linux-leds/20190705100851.zn2jkipj4fxq5we6@devuan/


Daniel.



> > Signed-off-by: Jean-Jacques Hiblot <jjhiblot@...com>
> > Signed-off-by: Corentin LABBE <clabbe@...libre.com>
> > ---
> >  drivers/video/backlight/led_bl.c | 13 +++++++++++++
> >  1 file changed, 13 insertions(+)
> > 
> > diff --git a/drivers/video/backlight/led_bl.c b/drivers/video/backlight/led_bl.c
> > index f54d256e2d54..ebd7acc32980 100644
> > --- a/drivers/video/backlight/led_bl.c
> > +++ b/drivers/video/backlight/led_bl.c
> > @@ -8,6 +8,7 @@
> >  
> >  #include <linux/backlight.h>
> >  #include <linux/leds.h>
> > +#include <linux/gpio.h>
> >  #include <linux/module.h>
> >  #include <linux/platform_device.h>
> >  
> > @@ -15,6 +16,7 @@ struct led_bl_data {
> >  	struct device		*dev;
> >  	struct backlight_device	*bl_dev;
> >  	struct led_classdev	**leds;
> > +	struct gpio_desc        *enable_gpio;
> >  	bool			enabled;
> >  	int			nb_leds;
> >  	unsigned int		*levels;
> > @@ -35,6 +37,9 @@ static void led_bl_set_brightness(struct led_bl_data *priv, int level)
> >  	for (i = 0; i < priv->nb_leds; i++)
> >  		led_set_brightness(priv->leds[i], bkl_brightness);
> >  
> > +	if (!priv->enabled)
> > +		gpiod_set_value_cansleep(priv->enable_gpio, 1);
> > +
> >  	priv->enabled = true;
> >  }
> >  
> > @@ -48,6 +53,9 @@ static void led_bl_power_off(struct led_bl_data *priv)
> >  	for (i = 0; i < priv->nb_leds; i++)
> >  		led_set_brightness(priv->leds[i], LED_OFF);
> >  
> > +	if (priv->enabled)
> > +		gpiod_set_value_cansleep(priv->enable_gpio, 0);
> > +
> >  	priv->enabled = false;
> >  }
> >  
> > @@ -209,6 +217,11 @@ static int led_bl_probe(struct platform_device *pdev)
> >  		return PTR_ERR(priv->bl_dev);
> >  	}
> >  
> > +	priv->enable_gpio = devm_gpiod_get_optional(&pdev->dev, "enable",
> > +						    GPIOD_OUT_LOW);
> > +	if (IS_ERR(priv->enable_gpio))
> > +		return PTR_ERR(priv->enable_gpio);
> > +
> >  	for (i = 0; i < priv->nb_leds; i++)
> >  		led_sysfs_disable(priv->leds[i]);
> >  
> > -- 
> > 2.25.1
> >