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From:   Jeremy Fertic <jeremyfertic@gmail.com>
To:     Jonathan Cameron <jic23@kernel.org>
Cc:     Lars-Peter Clausen <lars@metafoo.de>,
        Michael Hennerich <Michael.Hennerich@analog.com>,
        Hartmut Knaack <knaack.h@gmx.de>,
        Peter Meerwald-Stadler <pmeerw@pmeerw.net>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-iio@vger.kernel.org, devel@driverdev.osuosl.org,
        linux-kernel@vger.kernel.org,
        Jeremy Fertic <jeremyfertic@gmail.com>
Subject: [PATCH 06/11] staging: iio: adt7316: fix the dac write calculation
Date:   Tue, 11 Dec 2018 17:54:58 -0700
Message-Id: <20181212005503.28054-7-jeremyfertic@gmail.com>
In-Reply-To: <20181212005503.28054-1-jeremyfertic@gmail.com>
References: <20181212005503.28054-1-jeremyfertic@gmail.com>
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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.

Signed-off-by: Jeremy Fertic <jeremyfertic@gmail.com>
---
 drivers/staging/iio/addac/adt7316.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/staging/iio/addac/adt7316.c b/drivers/staging/iio/addac/adt7316.c
index b7d12d003ddc..77ef3c209b67 100644
--- a/drivers/staging/iio/addac/adt7316.c
+++ b/drivers/staging/iio/addac/adt7316.c
@@ -1442,7 +1442,7 @@ static ssize_t adt7316_show_DAC(struct adt7316_chip_info *chip,
 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;
 
@@ -1460,9 +1460,13 @@ static ssize_t adt7316_store_DAC(struct adt7316_chip_info *chip,
 		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;
 	}
-- 
2.19.1