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Commit 0d90ef87 authored by Marcus Folkesson's avatar Marcus Folkesson Committed by Greg Kroah-Hartman
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iio: adc: mcp3911: use correct formula for AD conversion 



commit 9e2238e3ae40d371a1130226e0e740aa1601efa6 upstream.

The ADC conversion is actually not rail-to-rail but with a factor 1.5.
Make use of this factor when calculating actual voltage.

Fixes: 3a89b289 ("iio: adc: add support for mcp3911")
Signed-off-by: default avatarMarcus Folkesson <marcus.folkesson@gmail.com>
Reviewed-by: default avatarAndy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20220722130726.7627-4-marcus.folkesson@gmail.com


Cc: <Stable@vger.kernel.org>
Signed-off-by: default avatarJonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent d186c655

drivers/iio/adc/mcp3911.c

+12 −5
Original line number Diff line number Diff line
@@ -38,8 +38,8 @@ 
#define MCP3911_CHANNEL(x)		(MCP3911_REG_CHANNEL0 + x * 3)

#define MCP3911_OFFCAL(x)		(MCP3911_REG_OFFCAL_CH0 + x * 6)



/* Internal voltage reference in uV */

#define MCP3911_INT_VREF_UV		1200000

/* Internal voltage reference in mV */

#define MCP3911_INT_VREF_MV		1200



#define MCP3911_REG_READ(reg, id)	((((reg) << 1) | ((id) << 5) | (1 << 0)) & 0xff)

#define MCP3911_REG_WRITE(reg, id)	((((reg) << 1) | ((id) << 5) | (0 << 0)) & 0xff)
@@ -137,11 +137,18 @@ static int mcp3911_read_raw(struct iio_dev *indio_dev, 


			*val = ret / 1000;

		} else {

			*val = MCP3911_INT_VREF_UV;

			*val = MCP3911_INT_VREF_MV;

		}



		*val2 = 24;

		ret = IIO_VAL_FRACTIONAL_LOG2;

		/*

		 * For 24bit Conversion

		 * Raw = ((Voltage)/(Vref) * 2^23 * Gain * 1.5

		 * Voltage = Raw * (Vref)/(2^23 * Gain * 1.5)

		 */



		/* val2 = (2^23 * 1.5) */

		*val2 = 12582912;

		ret = IIO_VAL_FRACTIONAL;

		break;

	}