Commit 347d7e45 authored by Stevens, Nick's avatar Stevens, Nick Committed by Guenter Roeck
Browse files

hwmon: (mcp3021) Fix broken output scaling 



The mcp3021 scaling code is dividing the VDD (full-scale) value in
millivolts by the A2D resolution to obtain the scaling factor. When VDD
is 3300mV (the standard value) and the resolution is 12-bit (4096
divisions), the result is a scale factor of 3300/4096, which is always
one.  Effectively, the raw A2D reading is always being returned because
no scaling is applied.

This patch fixes the issue and simplifies the register-to-volts
calculation, removing the unneeded "output_scale" struct member.

Signed-off-by: default avatarNick Stevens <Nick.Stevens@digi.com>
Cc: stable@vger.kernel.org # v3.10+
[Guenter Roeck: Dropped unnecessary value check]
Signed-off-by: default avatarGuenter Roeck <linux@roeck-us.net>
parent 56172d81

drivers/hwmon/mcp3021.c

+1 −13
Original line number Diff line number Diff line
@@ -31,14 +31,11 @@ 
/* output format */

#define MCP3021_SAR_SHIFT	2

#define MCP3021_SAR_MASK	0x3ff



#define MCP3021_OUTPUT_RES	10	/* 10-bit resolution */

#define MCP3021_OUTPUT_SCALE	4



#define MCP3221_SAR_SHIFT	0

#define MCP3221_SAR_MASK	0xfff

#define MCP3221_OUTPUT_RES	12	/* 12-bit resolution */

#define MCP3221_OUTPUT_SCALE	1



enum chips {

	mcp3021,
@@ -54,7 +51,6 @@ struct mcp3021_data { 
	u16 sar_shift;

	u16 sar_mask;

	u8 output_res;

	u8 output_scale;

};



static int mcp3021_read16(struct i2c_client *client)
@@ -84,13 +80,7 @@ static int mcp3021_read16(struct i2c_client *client) 


static inline u16 volts_from_reg(struct mcp3021_data *data, u16 val)

{

	if (val == 0)

		return 0;



	val = val * data->output_scale - data->output_scale / 2;



	return val * DIV_ROUND_CLOSEST(data->vdd,

			(1 << data->output_res) * data->output_scale);

	return DIV_ROUND_CLOSEST(data->vdd * val, 1 << data->output_res);

}



static ssize_t show_in_input(struct device *dev, struct device_attribute *attr,
@@ -132,14 +122,12 @@ static int mcp3021_probe(struct i2c_client *client, 
		data->sar_shift = MCP3021_SAR_SHIFT;

		data->sar_mask = MCP3021_SAR_MASK;

		data->output_res = MCP3021_OUTPUT_RES;

		data->output_scale = MCP3021_OUTPUT_SCALE;

		break;



	case mcp3221:

		data->sar_shift = MCP3221_SAR_SHIFT;

		data->sar_mask = MCP3221_SAR_MASK;

		data->output_res = MCP3221_OUTPUT_RES;

		data->output_scale = MCP3221_OUTPUT_SCALE;

		break;

	}

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