linux-kernel - [PATCH] backlight: gpio-backlight: use default-on on GPIO request

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Message-Id: <1445643883-30726-1-git-send-email-stefan@agner.ch>
Date:	Fri, 23 Oct 2015 16:44:43 -0700
From:	Stefan Agner <stefan@...er.ch>
To:	jingoohan1@...il.com, lee.jones@...aro.org
Cc:	linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	Stefan Agner <stefan@...er.ch>
Subject: [PATCH] backlight: gpio-backlight: use default-on on GPIO request

There are situations where the backlight should be on at boot time
(e.g. if the boot loader already turned the display on). The DT
bindings specify the "default-on" property for that purpose.
Currently, the initial state of the GPIO at request time is always
set to logical off (high or low depending on whether it is an
active high or low GPIO). Since the GPIO is requested as an output,
the GPIO will be driven low for a short period of time, which leads
to a flickering display in the above use-case.

Initialize the GPIO depending on the default-on property to be
logical on or off.

Signed-off-by: Stefan Agner <stefan@...er.ch>
---
 drivers/video/backlight/gpio_backlight.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/video/backlight/gpio_backlight.c b/drivers/video/backlight/gpio_backlight.c
index 5fbbc2e..1813441 100644
--- a/drivers/video/backlight/gpio_backlight.c
+++ b/drivers/video/backlight/gpio_backlight.c
@@ -89,6 +89,7 @@ static int gpio_backlight_probe(struct platform_device *pdev)
 	struct backlight_device *bl;
 	struct gpio_backlight *gbl;
 	struct device_node *np = pdev->dev.of_node;
+	unsigned long flags = GPIOF_DIR_OUT;
 	int ret;
 
 	if (!pdata && !np) {
@@ -114,9 +115,12 @@ static int gpio_backlight_probe(struct platform_device *pdev)
 		gbl->def_value = pdata->def_value;
 	}
 
-	ret = devm_gpio_request_one(gbl->dev, gbl->gpio, GPIOF_DIR_OUT |
-				    (gbl->active ? GPIOF_INIT_LOW
-						 : GPIOF_INIT_HIGH),
+	if (gbl->active)
+		flags |= gbl->def_value ? GPIOF_INIT_HIGH : GPIOF_INIT_LOW;
+	else
+		flags |= gbl->def_value ? GPIOF_INIT_LOW : GPIOF_INIT_HIGH;
+
+	ret = devm_gpio_request_one(gbl->dev, gbl->gpio, flags,
 				    pdata ? pdata->name : "backlight");
 	if (ret < 0) {
 		dev_err(&pdev->dev, "unable to request GPIO\n");
-- 
2.6.2

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