staging: iio: tsl2x7x: make proximity sensor function correctly

The bits for setting up the proximity diode were not setup correctly and
this was causing the proximity sensor to not function correctly. This
patch sets up the correct bit mask in tsl2x7x_chip_on() based on what
the data sheet expects. From page 35 of the TSL2771 data sheet:
https://ams.com/eng/content/download/250264/976045/file/TSL2771_DS000105_3-00.pdf

- Bits 0-1 is the ALS gain control
- Bits 2-3 is reserved (The proximity gain control on other tsl2x7x chips)
- Bits 4-5 is the proximity diode select
- Bits 6-7 is the LED drive strength

tsl2x7x_chip_on() had the power and diode hardcoded, so these are
extracted out into the settings so that these fields can be configured
in the platform data.

The default prox_gain is changed from 1 (2X gain) to 0 (1X gain) since
the proximity gain control on the TSL2771, TMD2771, and other chips have
these fields listed as reserved, and to write 0 into those bits.

Verified that the proximity sensor now works correctly on a TSL2771
hooked up to a Raspberry Pi 2.

Signed-off-by: Brian Masney <masneyb@onstation.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/staging/iio/light/tsl2x7x.c

@@ -109,15 +109,15 @@
 #define TSL2X7X_CNTL_INTPROXPON_ENBL	0x2F
 
 /*Prox diode to use */
-#define TSL2X7X_DIODE0			0x10
-#define TSL2X7X_DIODE1			0x20
-#define TSL2X7X_DIODE_BOTH		0x30
+#define TSL2X7X_DIODE0			0x01
+#define TSL2X7X_DIODE1			0x02
+#define TSL2X7X_DIODE_BOTH		0x03
 
 /* LED Power */
 #define TSL2X7X_100_mA			0x00
-#define TSL2X7X_50_mA			0x40
-#define TSL2X7X_25_mA			0x80
-#define TSL2X7X_13_mA			0xD0
+#define TSL2X7X_50_mA			0x01
+#define TSL2X7X_25_mA			0x02
+#define TSL2X7X_13_mA			0x03
 #define TSL2X7X_MAX_TIMER_CNT		0xFF
 
 #define TSL2X7X_MIN_ITIME		3
@@ -228,7 +228,7 @@ static const struct tsl2x7x_settings tsl2x7x_default_settings = {
 	.als_time = 219, /* 101 ms */
 	.als_gain = 0,
 	.prx_time = 254, /* 5.4 ms */
-	.prox_gain = 1,
+	.prox_gain = 0,
 	.wait_time = 245,
 	.prox_config = 0,
 	.als_gain_trim = 1000,
@@ -240,7 +240,9 @@ static const struct tsl2x7x_settings tsl2x7x_default_settings = {
 	.prox_thres_low  = 0,
 	.prox_thres_high = 512,
 	.prox_max_samples_cal = 30,
-	.prox_pulse_count = 8
+	.prox_pulse_count = 8,
+	.prox_diode = TSL2X7X_DIODE1,
+	.prox_power = TSL2X7X_100_mA
 };
 
 static const s16 tsl2x7x_als_gain[] = {
@@ -659,9 +661,10 @@ static int tsl2x7x_chip_on(struct iio_dev *indio_dev)
 
 	/* Set the gain based on tsl2x7x_settings struct */
 	chip->tsl2x7x_config[TSL2X7X_GAIN] =
-		chip->settings.als_gain |
-			(TSL2X7X_100_mA | TSL2X7X_DIODE1) |
-			(chip->settings.prox_gain << 2);
+		(chip->settings.als_gain & 0xFF) |
+		((chip->settings.prox_gain & 0xFF) << 2) |
+		(chip->settings.prox_diode << 4) |
+		(chip->settings.prox_power << 6);
 
 	/* set chip struct re scaling and saturation */
 	chip->als_saturation = als_count * 922; /* 90% of full scale */

drivers/staging/iio/light/tsl2x7x.h

@@ -78,6 +78,8 @@ struct tsl2x7x_settings {
 	int prox_thres_high;
 	int prox_pulse_count;
 	int prox_max_samples_cal;
+	int prox_diode;
+	int prox_power;
 };
 
 /**