[2/2] iio: adc: ti_am335x_tscadc: Improve accuracy of measurement
diff mbox series

Message ID 20181119064236.28902-3-vigneshr@ti.com
State New
Headers show
Series
  • tscadc: Couple of fixes
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Commit Message

Vignesh Raghavendra Nov. 19, 2018, 6:42 a.m. UTC
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 <vigneshr@ti.com>
---
 drivers/iio/adc/ti_am335x_adc.c      | 5 ++++-
 include/linux/mfd/ti_am335x_tscadc.h | 4 ++++
 2 files changed, 8 insertions(+), 1 deletion(-)

Comments

Jonathan Cameron Nov. 25, 2018, 1:46 p.m. UTC | #1
On Mon, 19 Nov 2018 12:12:36 +0530
Vignesh R <vigneshr@ti.com> wrote:

> 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 <vigneshr@ti.com>
Given the header changes in mfd and the fact not much is going on with this
driver in IIO at the moment, I'm happy for this to go through the mfd tree.

Acked-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Thanks,

Jonathan

> ---
>  drivers/iio/adc/ti_am335x_adc.c      | 5 ++++-
>  include/linux/mfd/ti_am335x_tscadc.h | 4 ++++
>  2 files changed, 8 insertions(+), 1 deletion(-)
> 
> 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)
Lee Jones Nov. 28, 2018, 9:14 a.m. UTC | #2
On Mon, 19 Nov 2018, Vignesh R wrote:

> 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 <vigneshr@ti.com>
> ---
>  drivers/iio/adc/ti_am335x_adc.c      | 5 ++++-

>  include/linux/mfd/ti_am335x_tscadc.h | 4 ++++

Acked-by: Lee Jones <lee.jones@linaro.org>
Jonathan Cameron Dec. 1, 2018, 3:04 p.m. UTC | #3
On Wed, 28 Nov 2018 09:14:32 +0000
Lee Jones <lee.jones@linaro.org> wrote:

> On Mon, 19 Nov 2018, Vignesh R wrote:
> 
> > 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 <vigneshr@ti.com>
> > ---
> >  drivers/iio/adc/ti_am335x_adc.c      | 5 ++++-  
> 
> >  include/linux/mfd/ti_am335x_tscadc.h | 4 ++++  
> 
> Acked-by: Lee Jones <lee.jones@linaro.org>
> 
I'll leave this for v2 given changes in the first patch.

My assumption is at the moment that both will go through mfd.
Shout Lee if you have other plans.

Jonathan
Lee Jones Dec. 3, 2018, 7:01 a.m. UTC | #4
On Sat, 01 Dec 2018, Jonathan Cameron wrote:

> On Wed, 28 Nov 2018 09:14:32 +0000
> Lee Jones <lee.jones@linaro.org> wrote:
> 
> > On Mon, 19 Nov 2018, Vignesh R wrote:
> > 
> > > 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 <vigneshr@ti.com>
> > > ---
> > >  drivers/iio/adc/ti_am335x_adc.c      | 5 ++++-  
> > 
> > >  include/linux/mfd/ti_am335x_tscadc.h | 4 ++++  
> > 
> > Acked-by: Lee Jones <lee.jones@linaro.org>
> > 
> I'll leave this for v2 given changes in the first patch.
> 
> My assumption is at the moment that both will go through mfd.
> Shout Lee if you have other plans.

I'm fine with that.

Patch
diff mbox series

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)