From: Vignesh R Date: Mon, 3 Dec 2018 08:01:18 +0000 (+0530) Subject: iio: adc: ti_am335x_tscadc: Improve accuracy of measurement X-Git-Tag: v5.0-rc3~43^2~23 X-Git-Url: https://git.kernel.dk/?p=linux-2.6-block.git;a=commitdiff_plain;h=4b3ab9372ffa569827c8f7b7ffc7b69ba544a3bd iio: adc: ti_am335x_tscadc: Improve accuracy of measurement When performing single ended measurements with TSCADC, its recommended to set negative input (SEL_INM_SWC_3_0) of ADC step to ADC's VREFN in the corresponding STEP_CONFIGx register. Also, the positive(SEL_RFP_SWC_2_0) and negative(SEL_RFM_SWC_1_0) reference voltage for ADC step needs to be set to VREFP and VREFN respectively in STEP_CONFIGx register. Without these changes, there may be variation of as much as ~2% in the ADC's digital output which is bad for precise measurement. Signed-off-by: Vignesh R Acked-by: Jonathan Cameron Signed-off-by: Lee Jones --- diff --git a/drivers/iio/adc/ti_am335x_adc.c b/drivers/iio/adc/ti_am335x_adc.c index cafb1dcadc48..9d984f2a8ba7 100644 --- a/drivers/iio/adc/ti_am335x_adc.c +++ b/drivers/iio/adc/ti_am335x_adc.c @@ -142,7 +142,10 @@ static void tiadc_step_config(struct iio_dev *indio_dev) stepconfig |= STEPCONFIG_MODE_SWCNT; tiadc_writel(adc_dev, REG_STEPCONFIG(steps), - stepconfig | STEPCONFIG_INP(chan)); + stepconfig | STEPCONFIG_INP(chan) | + STEPCONFIG_INM_ADCREFM | + STEPCONFIG_RFP_VREFP | + STEPCONFIG_RFM_VREFN); if (adc_dev->open_delay[i] > STEPDELAY_OPEN_MASK) { dev_warn(dev, "chan %d open delay truncating to 0x3FFFF\n", diff --git a/include/linux/mfd/ti_am335x_tscadc.h b/include/linux/mfd/ti_am335x_tscadc.h index b9a53e013bff..483168403ae5 100644 --- a/include/linux/mfd/ti_am335x_tscadc.h +++ b/include/linux/mfd/ti_am335x_tscadc.h @@ -78,6 +78,8 @@ #define STEPCONFIG_YNN BIT(8) #define STEPCONFIG_XNP BIT(9) #define STEPCONFIG_YPN BIT(10) +#define STEPCONFIG_RFP(val) ((val) << 12) +#define STEPCONFIG_RFP_VREFP (0x3 << 12) #define STEPCONFIG_INM_MASK (0xF << 15) #define STEPCONFIG_INM(val) ((val) << 15) #define STEPCONFIG_INM_ADCREFM STEPCONFIG_INM(8) @@ -86,6 +88,8 @@ #define STEPCONFIG_INP_AN4 STEPCONFIG_INP(4) #define STEPCONFIG_INP_ADCREFM STEPCONFIG_INP(8) #define STEPCONFIG_FIFO1 BIT(26) +#define STEPCONFIG_RFM(val) ((val) << 23) +#define STEPCONFIG_RFM_VREFN (0x3 << 23) /* Delay register */ #define STEPDELAY_OPEN_MASK (0x3FFFF << 0)