Re: [PATCH RFC] iio: mxs-lradc: add scaling to enable divide_by_two operation

Hector Palacios <hector.palacios@xxxxxxxx> · Wed, 3 Jul 2013 12:39:44 +0200

Dear Alexandre,

On 07/03/2013 12:25 PM, Alexandre Belloni wrote:
Dear Hector,

On 03/07/2013 12:06, Hector Palacios wrote:
Most LRADC channels have an optional divisor by two which allows
a maximum input voltage of VDDIO - 50mV. This patch adds the scaling
info flag to these channels (all except 7 -VBATT-, 10 -VDDIO- and
15 -VDD5V-) to allow enabled divide_by_two read operation.

Reference: http://www.spinics.net/lists/linux-iio/msg08876.html
Signed-off-by: Hector Palacios <hector.palacios@xxxxxxxx>
---
  drivers/staging/iio/adc/mxs-lradc.c | 52 +++++++++++++++++++++++--------------
  1 file changed, 33 insertions(+), 19 deletions(-)

diff --git a/drivers/staging/iio/adc/mxs-lradc.c b/drivers/staging/iio/adc/mxs-lradc.c
index 51f781f..4363bb6 100644
--- a/drivers/staging/iio/adc/mxs-lradc.c
+++ b/drivers/staging/iio/adc/mxs-lradc.c
@@ -197,6 +197,7 @@ struct mxs_lradc {
  #define	LRADC_CTRL1_LRADC_IRQ_OFFSET		0

  #define	LRADC_CTRL2				0x20
+#define LRADC_CTRL2_DIVIDE_BY_TWO_OFFSET	24
  #define	LRADC_CTRL2_TEMPSENSE_PWD		(1 << 15)

  #define	LRADC_STATUS				0x40
@@ -234,7 +235,7 @@ static int mxs_lradc_read_raw(struct iio_dev *iio_dev,
  	struct mxs_lradc *lradc = iio_priv(iio_dev);
  	int ret;

-	if (m != IIO_CHAN_INFO_RAW)
+	if (m != IIO_CHAN_INFO_RAW && m != IIO_CHAN_INFO_SCALE)
  		return -EINVAL;

  	/* Check for invalid channel */
@@ -262,6 +263,11 @@ static int mxs_lradc_read_raw(struct iio_dev *iio_dev,
  		lradc->base + LRADC_CTRL1 + STMP_OFFSET_REG_CLR);
  	writel(0xff, lradc->base + LRADC_CTRL0 + STMP_OFFSET_REG_CLR);

+	/* Enable DIVIDE_BY_TWO on channel 0 if reading scaled value */
+	if (IIO_CHAN_INFO_SCALE == m)
+		writel(1 << LRADC_CTRL2_DIVIDE_BY_TWO_OFFSET,
+		       lradc->base + LRADC_CTRL2 + STMP_OFFSET_REG_SET);
+
  	/* Clean the slot's previous content, then set new one. */
  	writel(LRADC_CTRL4_LRADCSELECT_MASK(0),
  		lradc->base + LRADC_CTRL4 + STMP_OFFSET_REG_CLR);
@@ -286,6 +292,10 @@ static int mxs_lradc_read_raw(struct iio_dev *iio_dev,
  	ret = IIO_VAL_INT;

  err:
+	/* Disable DIVIDE_BY_TWO on channel 0 if reading scaled value */
+	if (IIO_CHAN_INFO_SCALE == m)
+		writel(1 << LRADC_CTRL2_DIVIDE_BY_TWO_OFFSET,
+		       lradc->base + LRADC_CTRL2 + STMP_OFFSET_REG_CLR);
  	writel(LRADC_CTRL1_LRADC_IRQ_EN(0),
  		lradc->base + LRADC_CTRL1 + STMP_OFFSET_REG_CLR);

@@ -806,11 +816,11 @@ static const struct iio_buffer_setup_ops mxs_lradc_buffer_ops = {
   * Driver initialization
   */

-#define MXS_ADC_CHAN(idx, chan_type) {				\
+#define MXS_ADC_CHAN(idx, chan_type, info) {			\
  	.type = (chan_type),					\
  	.indexed = 1,						\
  	.scan_index = (idx),					\
-	.info_mask = IIO_CHAN_INFO_RAW_SEPARATE_BIT,		\
+	.info_mask = (info),					\
  	.channel = (idx),					\
  	.scan_type = {						\
  		.sign = 'u',					\
@@ -819,23 +829,27 @@ static const struct iio_buffer_setup_ops mxs_lradc_buffer_ops = {
  	},							\
  }

+#define RAW		IIO_CHAN_INFO_RAW_SEPARATE_BIT
+#define RAW_SCALED	(IIO_CHAN_INFO_RAW_SEPARATE_BIT |	\
+			 IIO_CHAN_INFO_SCALE_SEPARATE_BIT)
+
  static const struct iio_chan_spec mxs_lradc_chan_spec[] = {
-	MXS_ADC_CHAN(0, IIO_VOLTAGE),
-	MXS_ADC_CHAN(1, IIO_VOLTAGE),
-	MXS_ADC_CHAN(2, IIO_VOLTAGE),
-	MXS_ADC_CHAN(3, IIO_VOLTAGE),
-	MXS_ADC_CHAN(4, IIO_VOLTAGE),
-	MXS_ADC_CHAN(5, IIO_VOLTAGE),
-	MXS_ADC_CHAN(6, IIO_VOLTAGE),
-	MXS_ADC_CHAN(7, IIO_VOLTAGE),	/* VBATT */
-	MXS_ADC_CHAN(8, IIO_TEMP),	/* Temp sense 0 */
-	MXS_ADC_CHAN(9, IIO_TEMP),	/* Temp sense 1 */
-	MXS_ADC_CHAN(10, IIO_VOLTAGE),	/* VDDIO */
-	MXS_ADC_CHAN(11, IIO_VOLTAGE),	/* VTH */
-	MXS_ADC_CHAN(12, IIO_VOLTAGE),	/* VDDA */
-	MXS_ADC_CHAN(13, IIO_VOLTAGE),	/* VDDD */
-	MXS_ADC_CHAN(14, IIO_VOLTAGE),	/* VBG */
-	MXS_ADC_CHAN(15, IIO_VOLTAGE),	/* VDD5V */
+	MXS_ADC_CHAN(0, IIO_VOLTAGE, RAW_SCALED),
+	MXS_ADC_CHAN(1, IIO_VOLTAGE, RAW_SCALED),
+	MXS_ADC_CHAN(2, IIO_VOLTAGE, RAW_SCALED),
+	MXS_ADC_CHAN(3, IIO_VOLTAGE, RAW_SCALED),
+	MXS_ADC_CHAN(4, IIO_VOLTAGE, RAW_SCALED),
+	MXS_ADC_CHAN(5, IIO_VOLTAGE, RAW_SCALED),
+	MXS_ADC_CHAN(6, IIO_VOLTAGE, RAW_SCALED),
+	MXS_ADC_CHAN(7, IIO_VOLTAGE, RAW),		/* VBATT */
+	MXS_ADC_CHAN(8, IIO_TEMP, RAW_SCALED),		/* Temp sense 0 */
+	MXS_ADC_CHAN(9, IIO_TEMP, RAW_SCALED),		/* Temp sense 1 */
+	MXS_ADC_CHAN(10, IIO_VOLTAGE, RAW),		/* VDDIO */
+	MXS_ADC_CHAN(11, IIO_VOLTAGE, RAW_SCALED),	/* VTH */
+	MXS_ADC_CHAN(12, IIO_VOLTAGE, RAW_SCALED),	/* VDDA */
+	MXS_ADC_CHAN(13, IIO_VOLTAGE, RAW_SCALED),	/* VDDD */
+	MXS_ADC_CHAN(14, IIO_VOLTAGE, RAW_SCALED),	/* VBG */
+	MXS_ADC_CHAN(15, IIO_VOLTAGE, RAW),		/* VDD5V */
  };

  static void mxs_lradc_hw_init(struct mxs_lradc *lradc)


This is not how it is supposed to work. you should actually add
IIO_CHAN_INFO_SCALE_SEPARATE_BIT to all channels .info_mask_separate.

Then, you will get two files: in_voltageX_raw and in_voltageX_scale.
Userland should calculate in_voltageX_raw * in_voltageX_scale. So when
reading in_voltageX_scale, you actually want to read the current scale.
To set the scale, you'll have to implement a write_raw.

Also, it would probably be a good idea to expose a
in_voltageX_scale_available file.

Thanks, I totally misunderstood it.
One question: to implement a divisor by two what should I write to the scale? A 
decimal number like 0.5? And I guess I should return -EINVAL for any other value, right?


Best regards,
--
Hector Palacios
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