[PATCH 3.16 017/129] staging: iio: adt7316: fix the dac write calculation

[Ben Hutchings]

3.16.70-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Jeremy Fertic <jeremyfer...@gmail.com>

commit 78accaea117c1ae878774974fab91ac4a0b0e2b0 upstream.

The lsb calculation is not masking the correct bits from the user input.
Subtract 1 from (1 << offset) to correctly set up the mask to be applied
to user input.

The lsb register stores its value starting at the bit 7 position.
adt7316_store_DAC() currently assumes the value is at the other end of the
register. Shift the lsb value before storing it in a new variable lsb_reg,
and write this variable to the lsb register.

Fixes: 35f6b6b86ede ("staging: iio: new ADT7316/7/8 and ADT7516/7/9 driver")
Signed-off-by: Jeremy Fertic <jeremyfer...@gmail.com>
Signed-off-by: Jonathan Cameron <jonathan.came...@huawei.com>
Signed-off-by: Ben Hutchings <b...@decadent.org.uk>
---
 drivers/staging/iio/addac/adt7316.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

--- a/drivers/staging/iio/addac/adt7316.c
+++ b/drivers/staging/iio/addac/adt7316.c
@@ -1448,7 +1448,7 @@ static ssize_t adt7316_show_DAC(struct a
 static ssize_t adt7316_store_DAC(struct adt7316_chip_info *chip,
                int channel, const char *buf, size_t len)
 {
-       u8 msb, lsb, offset;
+       u8 msb, lsb, lsb_reg, offset;
        u16 data;
        int ret;
 
@@ -1466,9 +1466,13 @@ static ssize_t adt7316_store_DAC(struct
                return -EINVAL;
 
        if (chip->dac_bits > 8) {
-               lsb = data & (1 << offset);
+               lsb = data & ((1 << offset) - 1);
+               if (chip->dac_bits == 12)
+                       lsb_reg = lsb << ADT7316_DA_12_BIT_LSB_SHIFT;
+               else
+                       lsb_reg = lsb << ADT7316_DA_10_BIT_LSB_SHIFT;
                ret = chip->bus.write(chip->bus.client,
-                       ADT7316_DA_DATA_BASE + channel * 2, lsb);
+                       ADT7316_DA_DATA_BASE + channel * 2, lsb_reg);
                if (ret)
                        return -EIO;
        }