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

Daniel Thompson
2021-11-02T11:25:22Z

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@ti.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@ti.com>
> > Signed-off-by: Corentin LABBE <clabbe@baylibre.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
> >