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hwmon: (mcp3021) Fix broken output scaling

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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: Nick Stevens <Nick.Stevens@digi.com>
Cc: stable@vger.kernel.org # v3.10+
[Guenter Roeck: Dropped unnecessary value check]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
This commit is contained in:
Stevens, Nick 2015-07-01 16:07:41 +00:00 committed by Guenter Roeck
parent 56172d81a9
commit 347d7e45bd
1 changed files with 1 additions and 13 deletions
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14
drivers/hwmon/mcp3021.c
View file

@ -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;
}