[PATCH v2 13/17] leds: leds-nuc: better detect NUC6/NUC7 devices

[Mauro Carvalho Chehab]

There's no documented way to detect if the WMI API is valid,
as, when it is not valid, it just returns 4 zeros.

However, as having a value of 0x00 for the blinking state
is not valid, we can check for it at detection time, in
order to disable LEDs control on devices that won't
support it.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@xxxxxxxxxx>
---
 drivers/leds/leds-nuc.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/drivers/leds/leds-nuc.c b/drivers/leds/leds-nuc.c
index 6aa0bf16c8b7..af57f54cfb05 100644
--- a/drivers/leds/leds-nuc.c
+++ b/drivers/leds/leds-nuc.c
@@ -312,6 +312,13 @@ static int nuc_wmi_query_leds_nuc6(struct device *dev)
 		return ret;
 	}
 
+	/*
+	 * Detect if NUC6/NUC7 supports the WMI API by checking the
+	 * returned blink state, as valid values range from 0x01 to 0x07.
+	 */
+	if (output[1] == 0x00)
+		return -ENODEV;
+
 	led = &priv->led[priv->num_leds];
 	led->id = POWER_LED;
 	led->color_type = LED_BLUE_AMBER;
@@ -325,6 +332,14 @@ static int nuc_wmi_query_leds_nuc6(struct device *dev)
 		dev_warn(dev, "Get S0 Ring: error %d\n", ret);
 		return ret;
 	}
+
+	/*
+	 * Detect if NUC6/NUC7 supports the WMI API by checking the
+	 * returned blink state, as valid values range from 0x01 to 0x07.
+	 */
+	if (output[1] == 0x00)
+		return -ENODEV;
+
 	led = &priv->led[priv->num_leds];
 	led->id = RING_LED;
 	led->color_type = LED_BLUE_AMBER;
-- 
2.31.1