STAGING:iio:light: fix ISL29018 init to handle brownout

After a voltage brownout, sensor will now operate correctly.

Page 10 of ISL29018 data sheet and the Intersil Application Note 1534
describe the required initialization sequence:
1. Write 0x00 to register 0x08 (TEST)
2. Write 0x00 to register 0x00 (CMD1)
3. msleep(1)
4. program remaining registers as before

Signed-off-by: Grant Grundler <grundler@chromium.org>
Reviewed-by: Bryan Freed <bfreed@chromium.org>
Acked-by: Jonathan Cameron <jic23@cam.ac.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/staging/iio/light/isl29018.c b/drivers/staging/iio/light/isl29018.c
index 426b6af708073c03d85d63cf81fcb326f4f00ec9..da5bb33a66c1a1912a6cd32cec250a24616d7f68 100644 (file)
--- a/drivers/staging/iio/light/isl29018.c
+++ b/drivers/staging/iio/light/isl29018.c
@@ -53,6 +53,10 @@
 #define ISL29018_REG_ADD_DATA_MSB      0x03
 #define ISL29018_MAX_REGS              ISL29018_REG_ADD_DATA_MSB
 
+#define ISL29018_REG_TEST              0x08
+#define ISL29018_TEST_SHIFT            0
+#define ISL29018_TEST_MASK             (0xFF << ISL29018_TEST_SHIFT)
+
 struct isl29018_chip {
        struct i2c_client       *client;
        struct mutex            lock;
@@ -457,6 +461,48 @@ static int isl29018_chip_init(struct i2c_client *client)
 
        memset(chip->reg_cache, 0, sizeof(chip->reg_cache));
 
+       /* Code added per Intersil Application Note 1534:
+        *     When VDD sinks to approximately 1.8V or below, some of
+        * the part's registers may change their state. When VDD
+        * recovers to 2.25V (or greater), the part may thus be in an
+        * unknown mode of operation. The user can return the part to
+        * a known mode of operation either by (a) setting VDD = 0V for
+        * 1 second or more and then powering back up with a slew rate
+        * of 0.5V/ms or greater, or (b) via I2C disable all ALS/PROX
+        * conversions, clear the test registers, and then rewrite all
+        * registers to the desired values.
+        * ...
+        * FOR ISL29011, ISL29018, ISL29021, ISL29023
+        * 1. Write 0x00 to register 0x08 (TEST)
+        * 2. Write 0x00 to register 0x00 (CMD1)
+        * 3. Rewrite all registers to the desired values
+        *
+        * ISL29018 Data Sheet (FN6619.1, Feb 11, 2010) essentially says
+        * the same thing EXCEPT the data sheet asks for a 1ms delay after
+        * writing the CMD1 register.
+        */
+       status = isl29018_write_data(client, ISL29018_REG_TEST, 0,
+                               ISL29018_TEST_MASK, ISL29018_TEST_SHIFT);
+       if (status < 0) {
+               dev_err(&client->dev, "Failed to clear isl29018 TEST reg."
+                                       "(%d)\n", status);
+               return status;
+       }
+
+       /* See Intersil AN1534 comments above.
+        * "Operating Mode" (COMMAND1) register is reprogrammed when
+        * data is read from the device.
+        */
+       status = isl29018_write_data(client, ISL29018_REG_ADD_COMMAND1, 0,
+                               0xff, 0);
+       if (status < 0) {
+               dev_err(&client->dev, "Failed to clear isl29018 CMD1 reg."
+                                       "(%d)\n", status);
+               return status;
+       }
+
+       msleep(1);      /* per data sheet, page 10 */
+
        /* set defaults */
        status = isl29018_set_range(client, chip->range, &new_range);
        if (status < 0) {