[PATCH v2] iio: adc: at91-sama5d2_adc: add support for oversampling resolution

Eugen Hristev
2018-06-21T08:00:06Z

This implements oversampling support for the SAMA5d2 ADC device.
Enabling oversampling : OSR can improve resolution from 12 bits to
13 or 14 bits.
Changing the channel specification to have 14 bits, and we shift the value
1 bit to the left if we have oversampling for just one extra bit, and two
bits to the left if we have no oversampling (old support).
From this commit on, the converted values for all the voltage channels
change to 14 bits real data, with most insignificant two bits always zero
if oversampling is not enabled.
sysfs object oversampling_ratio has been enabled and
oversampling_ratio_available will list possible values (1 or 4 or 16) having
1 as default (no oversampling, 1 sample for each conversion).
Special care was required for the triggered buffer scenario (+ DMA), to
adjust the values accordingly.
Touchscreen measurements supported by this driver are not affected by
oversampling, they are still on 12 bits (scale handing is already included
in the driver).

Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>
---
Changes in v2:
- updated channel spec to 14 bits as reviewed by Jonathan.
This makes things much simpler, and no more INT_PLUS_MICRO values.
- tidy up the extra line which was forgotten there
- renamed 0SAMPLES macro to 1SAMPLES , which makes more sense (1 sample for
each conversion is the actual number we have). other OSR values are 4SAMPLES
or 16SAMPLES per conversion.
- made code a bit clearer to read by having a per array adjust function
instead of those ugly casts I was using in v1. This is needed to adjust
the values recieved from DMA for each u16 storage bits per conversion (shift
left or not according to OSR setting).

drivers/iio/adc/at91-sama5d2_adc.c | 189 ++++++++++++++++++++++++++++++++-----
1 file changed, 163 insertions(+), 26 deletions(-)

diff --git a/drivers/iio/adc/at91-sama5d2_adc.c b/drivers/iio/adc/at91-sama5d2_adc.c
index 58c4c2b..adf1d69 100644
--- a/drivers/iio/adc/at91-sama5d2_adc.c
+++ b/drivers/iio/adc/at91-sama5d2_adc.c
@@ -130,6 +130,15 @@
#define AT91_SAMA5D2_OVER 0x3c
/* Extended Mode Register */
#define AT91_SAMA5D2_EMR 0x40
+/* Extended Mode Register - Oversampling rate */
+#define AT91_SAMA5D2_EMR_OSR(V) ((V) << 16)
+#define AT91_SAMA5D2_EMR_OSR_MASK GENMASK(17, 16)
+#define AT91_SAMA5D2_EMR_OSR_1SAMPLES 0
+#define AT91_SAMA5D2_EMR_OSR_4SAMPLES 1
+#define AT91_SAMA5D2_EMR_OSR_16SAMPLES 2
+
+/* Extended Mode Register - Averaging on single trigger event */
+#define AT91_SAMA5D2_EMR_ASTE(V) ((V) << 20)
/* Compare Window Register */
#define AT91_SAMA5D2_CWR 0x44
/* Channel Gain Register */
@@ -248,6 +257,11 @@
#define AT91_HWFIFO_MAX_SIZE_STR "128"
#define AT91_HWFIFO_MAX_SIZE 128

+/* Possible values for oversampling ratio */
+#define AT91_OSR_1SAMPLES 1
+#define AT91_OSR_4SAMPLES 4
+#define AT91_OSR_16SAMPLES 16
+
#define AT91_SAMA5D2_CHAN_SINGLE(num, addr) \
{ \
.type = IIO_VOLTAGE, \
@@ -256,12 +270,13 @@
.scan_index = num, \
.scan_type = { \
.sign = 'u', \
- .realbits = 12, \
+ .realbits = 14, \
.storagebits = 16, \
}, \
.info_mask_separate = BIT(IIO_CHAN_INFO_RAW), \
.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE), \
- .info_mask_shared_by_all = BIT(IIO_CHAN_INFO_SAMP_FREQ),\
+ .info_mask_shared_by_all = BIT(IIO_CHAN_INFO_SAMP_FREQ)|\
+ BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO), \
.datasheet_name = "CH"#num, \
.indexed = 1, \
}
@@ -276,12 +291,13 @@
.scan_index = num + AT91_SAMA5D2_SINGLE_CHAN_CNT, \
.scan_type = { \
.sign = 's', \
- .realbits = 12, \
+ .realbits = 14, \
.storagebits = 16, \
}, \
.info_mask_separate = BIT(IIO_CHAN_INFO_RAW), \
.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE), \
- .info_mask_shared_by_all = BIT(IIO_CHAN_INFO_SAMP_FREQ),\
+ .info_mask_shared_by_all = BIT(IIO_CHAN_INFO_SAMP_FREQ)|\
+ BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO), \
.datasheet_name = "CH"#num"-CH"#num2, \
.indexed = 1, \
}
@@ -299,7 +315,8 @@
.storagebits = 16, \
}, \
.info_mask_separate = BIT(IIO_CHAN_INFO_RAW), \
- .info_mask_shared_by_all = BIT(IIO_CHAN_INFO_SAMP_FREQ),\
+ .info_mask_shared_by_all = BIT(IIO_CHAN_INFO_SAMP_FREQ)|\
+ BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO), \
.datasheet_name = name, \
}
#define AT91_SAMA5D2_CHAN_PRESSURE(num, name) \
@@ -313,7 +330,8 @@
.storagebits = 16, \
}, \
.info_mask_separate = BIT(IIO_CHAN_INFO_RAW), \
- .info_mask_shared_by_all = BIT(IIO_CHAN_INFO_SAMP_FREQ),\
+ .info_mask_shared_by_all = BIT(IIO_CHAN_INFO_SAMP_FREQ)|\
+ BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO), \
.datasheet_name = name, \
}

@@ -384,6 +402,7 @@ struct at91_adc_state {
const struct iio_chan_spec *chan;
bool conversion_done;
u32 conversion_value;
+ unsigned int oversampling_ratio;
struct at91_adc_soc_info soc_info;
wait_queue_head_t wq_data_available;
struct at91_adc_dma dma_st;
@@ -475,6 +494,77 @@ static inline int at91_adc_of_xlate(struct iio_dev *indio_dev,
return at91_adc_chan_xlate(indio_dev, iiospec->args[0]);
}

+static void at91_adc_config_emr(struct at91_adc_state *st)
+{
+ /* configure the extended mode register */
+ unsigned int emr = at91_adc_readl(st, AT91_SAMA5D2_EMR);
+
+ /* select oversampling per single trigger event */
+ emr |= AT91_SAMA5D2_EMR_ASTE(1);
+
+ /* delete leftover content if it's the case */
+ emr &= ~AT91_SAMA5D2_EMR_OSR_MASK;
+
+ /* select oversampling ratio from configuration */
+ switch (st->oversampling_ratio) {
+ case AT91_OSR_1SAMPLES:
+ emr |= AT91_SAMA5D2_EMR_OSR(AT91_SAMA5D2_EMR_OSR_1SAMPLES) &
+ AT91_SAMA5D2_EMR_OSR_MASK;
+ break;
+ case AT91_OSR_4SAMPLES:
+ emr |= AT91_SAMA5D2_EMR_OSR(AT91_SAMA5D2_EMR_OSR_4SAMPLES) &
+ AT91_SAMA5D2_EMR_OSR_MASK;
+ break;
+ case AT91_OSR_16SAMPLES:
+ emr |= AT91_SAMA5D2_EMR_OSR(AT91_SAMA5D2_EMR_OSR_16SAMPLES) &
+ AT91_SAMA5D2_EMR_OSR_MASK;
+ break;
+ };
+
+ at91_adc_writel(st, AT91_SAMA5D2_EMR, emr);
+}
+
+static int at91_adc_adjust_val_osr(struct at91_adc_state *st, int *val)
+{
+ if (st->oversampling_ratio == AT91_OSR_1SAMPLES) {
+ /*
+ * in this case we only have 12 bits of real data, but channel
+ * is registered as 14 bits, so shift left two bits
+ */
+ *val <<= 2;
+ } else if (st->oversampling_ratio == AT91_OSR_4SAMPLES) {
+ /*
+ * in this case we have 13 bits of real data, but channel
+ * is registered as 14 bits, so left shift one bit
+ */
+ *val <<= 1;
+ }
+
+ return IIO_VAL_INT;
+}
+
+static void at91_adc_adjust_val_osr_array(struct at91_adc_state *st, void *buf,
+ int len)
+{
+ int i = 0, val;
+ u16 *buf_u16 = (u16 *) buf;
+
+ /*
+ * We are converting each two bytes (each sample).
+ * First convert the byte based array to u16, and convert each sample
+ * separately.
+ * Each value is two bytes in an array of chars, so to not shift
+ * more than we need, save the value separately.
+ * len is in bytes, so divide by two to get number of samples.
+ */
+ while (i < len / 2) {
+ val = buf_u16[i];
+ at91_adc_adjust_val_osr(st, &val);
+ buf_u16[i] = val;
+ i++;
+ }
+}
+
static int at91_adc_configure_touch(struct at91_adc_state *st, bool state)
{
u32 clk_khz = st->current_sample_rate / 1000;
@@ -916,6 +1006,7 @@ static void at91_adc_trigger_handler_nodma(struct iio_dev *indio_dev,
{
struct at91_adc_state *st = iio_priv(indio_dev);
int i = 0;
+ int val;
u8 bit;

for_each_set_bit(bit, indio_dev->active_scan_mask,
@@ -936,7 +1027,9 @@ static void at91_adc_trigger_handler_nodma(struct iio_dev *indio_dev,
* Thus, emit a warning.
*/
if (chan->type == IIO_VOLTAGE) {
- st->buffer[i] = at91_adc_readl(st, chan->address);
+ val = at91_adc_readl(st, chan->address);
+ at91_adc_adjust_val_osr(st, &val);
+ st->buffer[i] = val;
} else {
st->buffer[i] = 0;
WARN(true, "This trigger cannot handle this type of channel");
@@ -972,6 +1065,14 @@ static void at91_adc_trigger_handler_dma(struct iio_dev *indio_dev)
interval = div_s64((ns - st->dma_st.dma_ts), sample_count);

while (transferred_len >= sample_size) {
+ /*
+ * for all the values in the current sample,
+ * adjust the values inside the buffer for oversampling
+ */
+ at91_adc_adjust_val_osr_array(st,
+ &st->dma_st.rx_buf[st->dma_st.buf_idx],
+ sample_size);
+
iio_push_to_buffers_with_timestamp(indio_dev,
(st->dma_st.rx_buf + st->dma_st.buf_idx),
(st->dma_st.dma_ts + interval * sample_index));
@@ -1212,7 +1313,7 @@ static int at91_adc_read_info_raw(struct iio_dev *indio_dev,
mutex_unlock(&st->lock);
iio_device_release_direct_mode(indio_dev);

- return ret;
+ return at91_adc_adjust_val_osr(st, val);
}
if (chan->type == IIO_PRESSURE) {
ret = iio_device_claim_direct_mode(indio_dev);
@@ -1225,7 +1326,7 @@ static int at91_adc_read_info_raw(struct iio_dev *indio_dev,
mutex_unlock(&st->lock);
iio_device_release_direct_mode(indio_dev);

- return ret;
+ return at91_adc_adjust_val_osr(st, val);
}

/* in this case we have a voltage channel */
@@ -1254,9 +1355,9 @@ static int at91_adc_read_info_raw(struct iio_dev *indio_dev,

if (ret > 0) {
*val = st->conversion_value;
+ ret = at91_adc_adjust_val_osr(st, val);
if (chan->scan_type.sign == 's')
*val = sign_extend32(*val, 11);
- ret = IIO_VAL_INT;
st->conversion_done = false;
}

@@ -1292,6 +1393,10 @@ static int at91_adc_read_raw(struct iio_dev *indio_dev,
*val = at91_adc_get_sample_freq(st);
return IIO_VAL_INT;

+ case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
+ *val = st->oversampling_ratio;
+ return IIO_VAL_INT;
+
default:
return -EINVAL;
}
@@ -1303,16 +1408,28 @@ static int at91_adc_write_raw(struct iio_dev *indio_dev,
{
struct at91_adc_state *st = iio_priv(indio_dev);

- if (mask != IIO_CHAN_INFO_SAMP_FREQ)
- return -EINVAL;
+ switch (mask) {
+ case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
+ if ((val != AT91_OSR_1SAMPLES) && (val != AT91_OSR_4SAMPLES) &&
+ (val != AT91_OSR_16SAMPLES))
+ return -EINVAL;
+ /* if no change, optimize out */
+ if (val == st->oversampling_ratio)
+ return 0;
+ st->oversampling_ratio = val;
+ /* update ratio */
+ at91_adc_config_emr(st);
+ return 0;
+ case IIO_CHAN_INFO_SAMP_FREQ:
+ if (val < st->soc_info.min_sample_rate ||
+ val > st->soc_info.max_sample_rate)
+ return -EINVAL;

- if (val < st->soc_info.min_sample_rate ||
- val > st->soc_info.max_sample_rate)
+ at91_adc_setup_samp_freq(st, val);
+ return 0;
+ default:
return -EINVAL;
-
- at91_adc_setup_samp_freq(st, val);
-
- return 0;
+ };
}

static void at91_adc_dma_init(struct platform_device *pdev)
@@ -1446,14 +1563,6 @@ static int at91_adc_update_scan_mode(struct iio_dev *indio_dev,
return 0;
}

-static const struct iio_info at91_adc_info = {
- .read_raw = &at91_adc_read_raw,
- .write_raw = &at91_adc_write_raw,
- .update_scan_mode = &at91_adc_update_scan_mode,
- .of_xlate = &at91_adc_of_xlate,
- .hwfifo_set_watermark = &at91_adc_set_watermark,
-};
-
static void at91_adc_hw_init(struct at91_adc_state *st)
{
at91_adc_writel(st, AT91_SAMA5D2_CR, AT91_SAMA5D2_CR_SWRST);
@@ -1466,6 +1575,9 @@ static void at91_adc_hw_init(struct at91_adc_state *st)
AT91_SAMA5D2_MR_TRANSFER(2) | AT91_SAMA5D2_MR_ANACH);

at91_adc_setup_samp_freq(st, st->soc_info.min_sample_rate);
+
+ /* configure extended mode register */
+ at91_adc_config_emr(st);
}

static ssize_t at91_adc_get_fifo_state(struct device *dev,
@@ -1496,6 +1608,20 @@ static IIO_DEVICE_ATTR(hwfifo_watermark, 0444,
static IIO_CONST_ATTR(hwfifo_watermark_min, "2");
static IIO_CONST_ATTR(hwfifo_watermark_max, AT91_HWFIFO_MAX_SIZE_STR);

+static IIO_CONST_ATTR(oversampling_ratio_available,
+ __stringify(AT91_OSR_1SAMPLES) " "
+ __stringify(AT91_OSR_4SAMPLES) " "
+ __stringify(AT91_OSR_16SAMPLES));
+
+static struct attribute *at91_adc_attributes[] = {
+ &iio_const_attr_oversampling_ratio_available.dev_attr.attr,
+ NULL,
+};
+
+static const struct attribute_group at91_adc_attribute_group = {
+ .attrs = at91_adc_attributes,
+};
+
static const struct attribute *at91_adc_fifo_attributes[] = {
&iio_const_attr_hwfifo_watermark_min.dev_attr.attr,
&iio_const_attr_hwfifo_watermark_max.dev_attr.attr,
@@ -1504,6 +1630,15 @@ static const struct attribute *at91_adc_fifo_attributes[] = {
NULL,
};

+static const struct iio_info at91_adc_info = {
+ .attrs = &at91_adc_attribute_group,
+ .read_raw = &at91_adc_read_raw,
+ .write_raw = &at91_adc_write_raw,
+ .update_scan_mode = &at91_adc_update_scan_mode,
+ .of_xlate = &at91_adc_of_xlate,
+ .hwfifo_set_watermark = &at91_adc_set_watermark,
+};
+
static int at91_adc_probe(struct platform_device *pdev)
{
struct iio_dev *indio_dev;
@@ -1532,6 +1667,8 @@ static int at91_adc_probe(struct platform_device *pdev)
bitmap_set(&st->touch_st.channels_bitmask,
AT91_SAMA5D2_TOUCH_P_CHAN_IDX, 1);

+ st->oversampling_ratio = AT91_OSR_1SAMPLES;
+
ret = of_property_read_u32(pdev->dev.of_node,
"atmel,min-sample-rate-hz",
&st->soc_info.min_sample_rate);
--
2.7.4