Hi Nick,
On Wed, Jul 01, 2015 at 04:07:41PM +0000, Stevens, Nick wrote:
> 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>
Code looks good. I'll apply it, with a minor change as mentioned below.
Thanks,
Guenter
> ---
>
> 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;
>
This check is no longer needed and can be dropped.
> - 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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