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iio: adc: stm32: add support for differential channels
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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 <[email protected]>
Signed-off-by: Jonathan Cameron <[email protected]>
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@jic23
Fabrice Gasnier authored and jic23 committed Dec 2, 2017
1 parent 0bae72a commit 3fb2e24
Showing 1 changed file with 103 additions and 20 deletions.
123 changes: 103 additions & 20 deletions drivers/iio/adc/stm32-adc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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

Expand Down Expand Up @@ -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
Expand Down Expand Up @@ -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
Expand All @@ -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
Expand Down Expand Up @@ -945,15 +953,19 @@ 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)
Expand Down Expand Up @@ -1225,10 +1237,23 @@ 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;
}
Expand Down Expand Up @@ -1591,47 +1616,80 @@ 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)
{
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 */
Expand All @@ -1652,18 +1710,43 @@ 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
* get either no value, 1 shared value for all indexes, or one
* 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;
Expand Down

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