| From 347d7e45bd09ce09cbc30d5cea9de377eb22f55c Mon Sep 17 00:00:00 2001 |
| From: "Stevens, Nick" <Nick.Stevens@digi.com> |
| Date: Wed, 1 Jul 2015 16:07:41 +0000 |
| Subject: hwmon: (mcp3021) Fix broken output scaling |
| |
| From: "Stevens, Nick" <Nick.Stevens@digi.com> |
| |
| commit 347d7e45bd09ce09cbc30d5cea9de377eb22f55c upstream. |
| |
| 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> |
| [Guenter Roeck: Dropped unnecessary value check] |
| Signed-off-by: Guenter Roeck <linux@roeck-us.net> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| drivers/hwmon/mcp3021.c | 14 +------------- |
| 1 file changed, 1 insertion(+), 13 deletions(-) |
| |
| --- 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) |
| @@ -84,13 +80,7 @@ static int mcp3021_read16(struct i2c_cli |
| |
| 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_clie |
| 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; |
| } |
| |