backlight: pwm: Reject legacy PWM request for device defined in DT

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 <dbaryshkov@gmail.com>
Signed-off-by: Vladimir Zapolskiy <vladimir_zapolskiy@mentor.com>
Acked-by: Thierry Reding <thierry.reding@gmail.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Tested-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

1 files changed, 9 insertions, 10 deletions

diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
index eff379b234cc..ae3c6b6fd5db 100644
--- a/drivers/video/backlight/pwm_bl.c
+++ b/drivers/video/backlight/pwm_bl.c
@@ -271,19 +271,18 @@ static int pwm_backlight_probe(struct platform_device *pdev)
         }
 
         pb->pwm = devm_pwm_get(&pdev->dev, NULL);
-        if (IS_ERR(pb->pwm)) {
-                ret = PTR_ERR(pb->pwm);
-                if (ret == -EPROBE_DEFER)
-                        goto err_alloc;
-
+        if (IS_ERR(pb->pwm) && PTR_ERR(pb->pwm) != -EPROBE_DEFER
+            && !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)) {
+                ret = PTR_ERR(pb->pwm);
+                if (ret != -EPROBE_DEFER)
+                        dev_err(&pdev->dev, "unable to request PWM\n");
+                goto err_alloc;
         }
 
         dev_dbg(&pdev->dev, "got pwm for backlight\n");