Platform PWM backlight data provided by board's device tree should be
complete enough to successfully request a pwm device using pwm_get()
API. This change fixes a bug, when an arbitrary (first found) PWM is
connected to a "pwm-backlight" compatible device, when explicit PWM
device reference is not given.

Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt
already describes "pwms" as a required property, instead of blind
selection of a potentially wrong PWM reject legacy PWM device
registration request, leave legacy API only for non-dt cases.

Based on initial implementation done by Dmitry Eremin-Solenikov.

Reported-by: Dmitry Eremin-Solenikov <redacted>
Signed-off-by: Vladimir Zapolskiy <redacted>
Acked-by: Thierry Reding <redacted>
---
 drivers/video/backlight/pwm_bl.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
index 57cb9ec..9991cdb 100644
--- a/drivers/video/backlight/pwm_bl.c
+++ b/drivers/video/backlight/pwm_bl.c

@@ -271,15 +271,16 @@ static int pwm_backlight_probe(struct platform_device *pdev)
 	}
 
 	pb->pwm = devm_pwm_get(&pdev->dev, NULL);
-	if (IS_ERR(pb->pwm)) {
+	if (IS_ERR(pb->pwm) && !pdev->dev.of_node) {
 		dev_err(&pdev->dev, "unable to request PWM, trying legacy API\n");
 		pb->legacy = true;
 		pb->pwm = pwm_request(data->pwm_id, "pwm-backlight");
-		if (IS_ERR(pb->pwm)) {
-			dev_err(&pdev->dev, "unable to request legacy PWM\n");
-			ret = PTR_ERR(pb->pwm);
-			goto err_alloc;
-		}
+	}
+
+	if (IS_ERR(pb->pwm)) {
+		dev_err(&pdev->dev, "unable to request PWM\n");
+		ret = PTR_ERR(pb->pwm);
+		goto err_alloc;
 	}
 
 	dev_dbg(&pdev->dev, "got pwm for backlight\n");