linux-kernel - [PATCH v2] backlight: pwm_bl: Fix GPIO out for unimplemented .get

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Date:   Tue,  4 Apr 2017 12:54:35 +0200
From:   Geert Uytterhoeven <geert+renesas@...der.be>
To:     Lee Jones <lee.jones@...aro.org>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Jingoo Han <jingoohan1@...il.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Peter Ujfalusi <peter.ujfalusi@...com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        linux-pwm@...r.kernel.org, linux-fbdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Geert Uytterhoeven <geert+renesas@...der.be>
Subject: [PATCH v2] backlight: pwm_bl: Fix GPIO out for unimplemented .get_direction()

Commit 7613c922315e308a ("backlight: pwm_bl: Move the checks for initial
power state to a separate function") not just moved some code, but made
slight changes in semantics.

If a gpiochip doesn't implement the optional .get_direction() callback,
gpiod_get_direction always returns -EINVAL, which is never equal to
GPIOF_DIR_IN, leading to the GPIO not being configured for output.

To avoid this, invert the test and check for not GPIOF_DIR_OUT instead,
like the original code did.

This restores the display on r8a7740/armadillo.

Fixes: 7613c922315e308a ("backlight: pwm_bl: Move the checks for initial power state to a separate function")
Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
Reviewed-by: Peter Ujfalusi <peter.ujfalusi@...com>
Acked-by: Philipp Zabel <p.zabel@...gutronix.de>
Acked-by: Daniel Thompson <daniel.thompson@...aro.org>
---
This fixes a regression introduced in v4.11-rc1.

v2:
  - Add Reviewed-by, Acked-by.

 drivers/video/backlight/pwm_bl.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
index d7efcb632f7d9dde..002f1ce22bd02032 100644
--- a/drivers/video/backlight/pwm_bl.c
+++ b/drivers/video/backlight/pwm_bl.c
@@ -297,14 +297,15 @@ static int pwm_backlight_probe(struct platform_device *pdev)
 	}
 
 	/*
-	 * If the GPIO is configured as input, change the direction to output
-	 * and set the GPIO as active.
+	 * If the GPIO is not known to be already configured as output, that
+	 * is, if gpiod_get_direction returns either GPIOF_DIR_IN or -EINVAL,
+	 * change the direction to output and set the GPIO as active.
 	 * Do not force the GPIO to active when it was already output as it
 	 * could cause backlight flickering or we would enable the backlight too
 	 * early. Leave the decision of the initial backlight state for later.
 	 */
 	if (pb->enable_gpio &&
-	    gpiod_get_direction(pb->enable_gpio) == GPIOF_DIR_IN)
+	    gpiod_get_direction(pb->enable_gpio) != GPIOF_DIR_OUT)
 		gpiod_direction_output(pb->enable_gpio, 1);
 
 	pb->power_supply = devm_regulator_get(&pdev->dev, "power");
-- 
2.7.4