linux-kernel - [PATCH v6 3/9] backlight: gpio: explicitly set the direction of the GPIO

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Message-Id: <20191019083556.19466-4-brgl@bgdev.pl>
Date:   Sat, 19 Oct 2019 10:35:50 +0200
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>,
        Lee Jones <lee.jones@...aro.org>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Jingoo Han <jingoohan1@...il.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Jacopo Mondi <jacopo@...ndi.org>
Cc:     linux-sh@...r.kernel.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Subject: [PATCH v6 3/9] backlight: gpio: explicitly set the direction of the GPIO

From: Bartosz Golaszewski <bgolaszewski@...libre.com>

The GPIO backlight driver currently requests the line 'as is', without
acively setting its direction. This can lead to problems: if the line
is in input mode by default, we won't be able to drive it later when
updating the status and also reading its initial value doesn't make
sense for backlight setting.

Request the line 'as is' initially, so that we can read its value
without affecting it but then change the direction to output explicitly
when setting the initial brightness.

Also: check the current direction and only read the value if it's output.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@...libre.com>
---
 drivers/video/backlight/gpio_backlight.c | 23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/drivers/video/backlight/gpio_backlight.c b/drivers/video/backlight/gpio_backlight.c
index 3955b513f2f8..a36ac3a45b81 100644
--- a/drivers/video/backlight/gpio_backlight.c
+++ b/drivers/video/backlight/gpio_backlight.c
@@ -25,9 +25,8 @@ struct gpio_backlight {
 	int def_value;
 };
 
-static int gpio_backlight_update_status(struct backlight_device *bl)
+static int gpio_backlight_get_curr_brightness(struct backlight_device *bl)
 {
-	struct gpio_backlight *gbl = bl_get_data(bl);
 	int brightness = bl->props.brightness;
 
 	if (bl->props.power != FB_BLANK_UNBLANK ||
@@ -35,6 +34,14 @@ static int gpio_backlight_update_status(struct backlight_device *bl)
 	    bl->props.state & (BL_CORE_SUSPENDED | BL_CORE_FBBLANK))
 		brightness = 0;
 
+	return brightness;
+}
+
+static int gpio_backlight_update_status(struct backlight_device *bl)
+{
+	struct gpio_backlight *gbl = bl_get_data(bl);
+	int brightness = gpio_backlight_get_curr_brightness(bl);
+
 	gpiod_set_value_cansleep(gbl->gpiod, brightness);
 
 	return 0;
@@ -85,7 +92,8 @@ static int gpio_backlight_initial_power_state(struct gpio_backlight *gbl)
 		return gbl->def_value ? FB_BLANK_UNBLANK : FB_BLANK_POWERDOWN;
 
 	/* if the enable GPIO is disabled, do not enable the backlight */
-	if (gpiod_get_value_cansleep(gbl->gpiod) == 0)
+	if (gpiod_get_direction(gbl->gpiod) == 0 &&
+	    gpiod_get_value_cansleep(gbl->gpiod) == 0)
 		return FB_BLANK_POWERDOWN;
 
 	return FB_BLANK_UNBLANK;
@@ -98,7 +106,7 @@ static int gpio_backlight_probe(struct platform_device *pdev)
 	struct backlight_properties props;
 	struct backlight_device *bl;
 	struct gpio_backlight *gbl;
-	int ret;
+	int ret, init_brightness;
 
 	gbl = devm_kzalloc(&pdev->dev, sizeof(*gbl), GFP_KERNEL);
 	if (gbl == NULL)
@@ -151,7 +159,12 @@ static int gpio_backlight_probe(struct platform_device *pdev)
 	bl->props.power = gpio_backlight_initial_power_state(gbl);
 	bl->props.brightness = 1;
 
-	backlight_update_status(bl);
+	init_brightness = gpio_backlight_get_curr_brightness(bl);
+	ret = gpiod_direction_output(gbl->gpiod, init_brightness);
+	if (ret) {
+		dev_err(&pdev->dev, "failed to set initial brightness\n");
+		return ret;
+	}
 
 	platform_set_drvdata(pdev, bl);
 	return 0;
-- 
2.23.0