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@xxxxxxxx>
---
Changes since v1:
* Simplify calculation based on discussion with Guenter Roeck
<linux@xxxxxxxxxxxx>
* Remove "output_scale" struct member made obsolete by simplifying
calculation
drivers/hwmon/mcp3021.c | 11 +----------
1 file changed, 1 insertion(+), 10 deletions(-)
diff --git a/drivers/hwmon/mcp3021.c b/drivers/hwmon/mcp3021.c
index d219c06..4f6b053 100644
--- a/drivers/hwmon/mcp3021.c
+++ b/drivers/hwmon/mcp3021.c
@@ -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)
@@ -87,10 +83,7 @@ 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 +125,12 @@ 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;
}
--
2.2.0
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