iio: dac: mcp4725: add missing powerdown bits in store eeprom

When issuing the write DAC register and write eeprom command, the two
powerdown bits (PD0 and PD1) are assumed by the chip to be present in
the bytes sent. Leaving them at 0 implies "powerdown disabled" which is
a different state that the current one. By adding the current state of
the powerdown in the i2c write, the chip will correctly power-on exactly
like as it is at the moment of store_eeprom call.

This is documented in MCP4725's datasheet, FIGURE 6-2: "Write Commands
for DAC Input Register and EEPROM" and MCP4726's datasheet, FIGURE 6-3:
"Write All Memory Command".

Signed-off-by: Jean-Francois Dagenais <jeff.dagenais@gmail.com>
Acked-by: Peter Meerwald-Stadler <pmeerw@pmeerw.net>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

diff --git a/drivers/iio/dac/mcp4725.c b/drivers/iio/dac/mcp4725.c
index 6d71fd905e29d69b0a5b1afa99c5451037333153..c701a45469f6436746b8c7e7b2da0680c45829ec 100644 (file)
--- a/drivers/iio/dac/mcp4725.c
+++ b/drivers/iio/dac/mcp4725.c
@@ -92,6 +92,7 @@ static ssize_t mcp4725_store_eeprom(struct device *dev,
 
        inoutbuf[0] = 0x60; /* write EEPROM */
        inoutbuf[0] |= data->ref_mode << 3;
+       inoutbuf[0] |= data->powerdown ? ((data->powerdown_mode + 1) << 1) : 0;
        inoutbuf[1] = data->dac_value >> 4;
        inoutbuf[2] = (data->dac_value & 0xf) << 4;