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Subject[PATCH v2 3/3] iio: adc: stm32: add support for differential channels
Date
STM32H7 ADC channels can be configured either as single ended or
differential with 'st,adc-channels' or 'st,adc-diff-channels'
(positive and negative input pair: <vinp vinn>, ...).

Differential channels have different offset and scale, from spec:
raw value = (full_scale / 2) * (1 + (vinp - vinn) / vref).
Add offset attribute.

Differential channels are selected by DIFSEL register. Negative
inputs must be added to pre-selected channels as well (PCSEL).

Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>
---
Changes in v2:
- Improve val & val2 variable names in stm32_adc_chan_init_one()
definition as suggested by Jonathan.
---
drivers/iio/adc/stm32-adc.c | 123 +++++++++++++++++++++++++++++++++++++-------
1 file changed, 103 insertions(+), 20 deletions(-)

diff --git a/drivers/iio/adc/stm32-adc.c b/drivers/iio/adc/stm32-adc.c
index 417a894..fd50067 100644
--- a/drivers/iio/adc/stm32-adc.c
+++ b/drivers/iio/adc/stm32-adc.c
@@ -92,6 +92,7 @@
#define STM32H7_ADC_SQR3 0x38
#define STM32H7_ADC_SQR4 0x3C
#define STM32H7_ADC_DR 0x40
+#define STM32H7_ADC_DIFSEL 0xC0
#define STM32H7_ADC_CALFACT 0xC4
#define STM32H7_ADC_CALFACT2 0xC8

@@ -154,7 +155,7 @@ enum stm32h7_adc_dmngt {
#define STM32H7_BOOST_CLKRATE 20000000UL

#define STM32_ADC_CH_MAX 20 /* max number of channels */
-#define STM32_ADC_CH_SZ 5 /* max channel name size */
+#define STM32_ADC_CH_SZ 10 /* max channel name size */
#define STM32_ADC_MAX_SQ 16 /* SQ1..SQ16 */
#define STM32_ADC_MAX_SMP 7 /* SMPx range is [0..7] */
#define STM32_ADC_TIMEOUT_US 100000
@@ -299,6 +300,7 @@ struct stm32_adc_cfg {
* @rx_buf: dma rx buffer cpu address
* @rx_dma_buf: dma rx buffer bus address
* @rx_buf_sz: dma rx buffer size
+ * @difsel bitmask to set single-ended/differential channel
* @pcsel bitmask to preselect channels on some devices
* @smpr_val: sampling time settings (e.g. smpr1 / smpr2)
* @cal: optional calibration data on some devices
@@ -321,12 +323,18 @@ struct stm32_adc {
u8 *rx_buf;
dma_addr_t rx_dma_buf;
unsigned int rx_buf_sz;
+ u32 difsel;
u32 pcsel;
u32 smpr_val[2];
struct stm32_adc_calib cal;
char chan_name[STM32_ADC_CH_MAX][STM32_ADC_CH_SZ];
};

+struct stm32_adc_diff_channel {
+ u32 vinp;
+ u32 vinn;
+};
+
/**
* struct stm32_adc_info - stm32 ADC, per instance config data
* @max_channels: Number of channels
@@ -944,15 +952,19 @@ static int stm32h7_adc_selfcalib(struct stm32_adc *adc)
* stm32h7_adc_prepare() - Leave power down mode to enable ADC.
* @adc: stm32 adc instance
* Leave power down mode.
+ * Configure channels as single ended or differential before enabling ADC.
* Enable ADC.
* Restore calibration data.
- * Pre-select channels that may be used in PCSEL (required by input MUX / IO).
+ * Pre-select channels that may be used in PCSEL (required by input MUX / IO):
+ * - Only one input is selected for single ended (e.g. 'vinp')
+ * - Two inputs are selected for differential channels (e.g. 'vinp' & 'vinn')
*/
static int stm32h7_adc_prepare(struct stm32_adc *adc)
{
int ret;

stm32h7_adc_exit_pwr_down(adc);
+ stm32_adc_writel(adc, STM32H7_ADC_DIFSEL, adc->difsel);

ret = stm32h7_adc_enable(adc);
if (ret)
@@ -1224,10 +1236,23 @@ static int stm32_adc_read_raw(struct iio_dev *indio_dev,
return ret;

case IIO_CHAN_INFO_SCALE:
- *val = adc->common->vref_mv;
- *val2 = chan->scan_type.realbits;
+ if (chan->differential) {
+ *val = adc->common->vref_mv * 2;
+ *val2 = chan->scan_type.realbits;
+ } else {
+ *val = adc->common->vref_mv;
+ *val2 = chan->scan_type.realbits;
+ }
return IIO_VAL_FRACTIONAL_LOG2;

+ case IIO_CHAN_INFO_OFFSET:
+ if (chan->differential)
+ /* ADC_full_scale / 2 */
+ *val = -((1 << chan->scan_type.realbits) / 2);
+ else
+ *val = 0;
+ return IIO_VAL_INT;
+
default:
return -EINVAL;
}
@@ -1591,29 +1616,39 @@ static void stm32_adc_smpr_init(struct stm32_adc *adc, int channel, u32 smp_ns)

static void stm32_adc_chan_init_one(struct iio_dev *indio_dev,
struct iio_chan_spec *chan, u32 vinp,
- int scan_index, u32 smp)
+ u32 vinn, int scan_index, bool differential)
{
struct stm32_adc *adc = iio_priv(indio_dev);
char *name = adc->chan_name[vinp];

chan->type = IIO_VOLTAGE;
chan->channel = vinp;
- snprintf(name, STM32_ADC_CH_SZ, "in%d", vinp);
+ if (differential) {
+ chan->differential = 1;
+ chan->channel2 = vinn;
+ snprintf(name, STM32_ADC_CH_SZ, "in%d-in%d", vinp, vinn);
+ } else {
+ snprintf(name, STM32_ADC_CH_SZ, "in%d", vinp);
+ }
chan->datasheet_name = name;
chan->scan_index = scan_index;
chan->indexed = 1;
chan->info_mask_separate = BIT(IIO_CHAN_INFO_RAW);
- chan->info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE);
+ chan->info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE) |
+ BIT(IIO_CHAN_INFO_OFFSET);
chan->scan_type.sign = 'u';
chan->scan_type.realbits = adc->cfg->adc_info->resolutions[adc->res];
chan->scan_type.storagebits = 16;
chan->ext_info = stm32_adc_ext_info;

- /* Prepare sampling time settings */
- stm32_adc_smpr_init(adc, chan->channel, smp);
-
/* pre-build selected channels mask */
adc->pcsel |= BIT(chan->channel);
+ if (differential) {
+ /* pre-build diff channels mask */
+ adc->difsel |= BIT(chan->channel);
+ /* Also add negative input to pre-selected channels */
+ adc->pcsel |= BIT(chan->channel2);
+ }
}

static int stm32_adc_chan_of_init(struct iio_dev *indio_dev)
@@ -1621,17 +1656,40 @@ static int stm32_adc_chan_of_init(struct iio_dev *indio_dev)
struct device_node *node = indio_dev->dev.of_node;
struct stm32_adc *adc = iio_priv(indio_dev);
const struct stm32_adc_info *adc_info = adc->cfg->adc_info;
+ struct stm32_adc_diff_channel diff[STM32_ADC_CH_MAX];
struct property *prop;
const __be32 *cur;
struct iio_chan_spec *channels;
- int scan_index = 0, num_channels, ret;
+ int scan_index = 0, num_channels = 0, num_diff = 0, ret, i;
u32 val, smp = 0;

- num_channels = of_property_count_u32_elems(node, "st,adc-channels");
- if (num_channels < 0 ||
- num_channels > adc_info->max_channels) {
+ ret = of_property_count_u32_elems(node, "st,adc-channels");
+ if (ret > adc_info->max_channels) {
dev_err(&indio_dev->dev, "Bad st,adc-channels?\n");
- return num_channels < 0 ? num_channels : -EINVAL;
+ return -EINVAL;
+ } else if (ret > 0) {
+ num_channels += ret;
+ }
+
+ ret = of_property_count_elems_of_size(node, "st,adc-diff-channels",
+ sizeof(*diff));
+ if (ret > adc_info->max_channels) {
+ dev_err(&indio_dev->dev, "Bad st,adc-diff-channels?\n");
+ return -EINVAL;
+ } else if (ret > 0) {
+ int size = ret * sizeof(*diff) / sizeof(u32);
+
+ num_diff = ret;
+ num_channels += ret;
+ ret = of_property_read_u32_array(node, "st,adc-diff-channels",
+ (u32 *)diff, size);
+ if (ret)
+ return ret;
+ }
+
+ if (!num_channels) {
+ dev_err(&indio_dev->dev, "No channels configured\n");
+ return -ENODATA;
}

/* Optional sample time is provided either for each, or all channels */
@@ -1652,6 +1710,33 @@ static int stm32_adc_chan_of_init(struct iio_dev *indio_dev)
return -EINVAL;
}

+ /* Channel can't be configured both as single-ended & diff */
+ for (i = 0; i < num_diff; i++) {
+ if (val == diff[i].vinp) {
+ dev_err(&indio_dev->dev,
+ "channel %d miss-configured\n", val);
+ return -EINVAL;
+ }
+ }
+ stm32_adc_chan_init_one(indio_dev, &channels[scan_index], val,
+ 0, scan_index, false);
+ scan_index++;
+ }
+
+ for (i = 0; i < num_diff; i++) {
+ if (diff[i].vinp >= adc_info->max_channels ||
+ diff[i].vinn >= adc_info->max_channels) {
+ dev_err(&indio_dev->dev, "Invalid channel in%d-in%d\n",
+ diff[i].vinp, diff[i].vinn);
+ return -EINVAL;
+ }
+ stm32_adc_chan_init_one(indio_dev, &channels[scan_index],
+ diff[i].vinp, diff[i].vinn, scan_index,
+ true);
+ scan_index++;
+ }
+
+ for (i = 0; i < scan_index; i++) {
/*
* Using of_property_read_u32_index(), smp value will only be
* modified if valid u32 value can be decoded. This allows to
@@ -1659,11 +1744,9 @@ static int stm32_adc_chan_of_init(struct iio_dev *indio_dev)
* value per channel.
*/
of_property_read_u32_index(node, "st,min-sample-time-nsecs",
- scan_index, &smp);
-
- stm32_adc_chan_init_one(indio_dev, &channels[scan_index],
- val, scan_index, smp);
- scan_index++;
+ i, &smp);
+ /* Prepare sampling time settings */
+ stm32_adc_smpr_init(adc, channels[i].channel, smp);
}

indio_dev->num_channels = scan_index;
--
1.9.1
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