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SubjectRe: [PATCH v2 3/3] iio: adc: stm32: add support for differential channels
On Wed, 25 Oct 2017 11:27:45 +0200
Fabrice Gasnier <fabrice.gasnier@st.com> wrote:

> 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>

Looks good. Again, DT review needed before I take the whole series.

Jonathan

> ---
> 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;

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