Re: [PATCH 3/3] iio: adc: stm32: add support for differential channels

From: Fabrice Gasnier
Date: Mon Oct 23 2017 - 04:10:44 EST

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On 10/21/2017 09:25 PM, Jonathan Cameron wrote:
> On Tue, 17 Oct 2017 15:15:45 +0200
> Fabrice Gasnier <fabrice.gasnier@xxxxxx> 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@xxxxxx>
> Looks fine to me. Will wait to see what others think on the binding in
> particular. I suppose that given we allow control over which single ended
> channels are registered, it makes sense to do it for differential channels
> as well.
>
> Thanks,
>
> 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 c95e6f7..cc7ca50 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 val,
>> - int scan_index, u32 smp)
>> + u32 val2, int scan_index, bool differential)
> val and val2 are slightly odd names in here.

Hi Jonathan,

You're right. I suppose vinp and vinn would be better names. This would
also better match with reference manual.

I'll update this in v2.

Thanks!
Best Regards,
Fabrice

>> {
>> struct stm32_adc *adc = iio_priv(indio_dev);
>> char *name = adc->chan_name[val];
>>
>> chan->type = IIO_VOLTAGE;
>> chan->channel = val;
>> - snprintf(name, STM32_ADC_CH_SZ, "in%d", val);
>> + if (differential) {
>> + chan->differential = 1;
>> + chan->channel2 = val2;
>> + snprintf(name, STM32_ADC_CH_SZ, "in%d-in%d", val, val2);
>> + } else {
>> + snprintf(name, STM32_ADC_CH_SZ, "in%d", val);
>> + }
>> 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;
>

Next message: Jerome Brunet: "Re: [PATCH] firmware: meson-sm: use generic compatible"
Previous message: Michal Hocko: "Re: [PATCH 1/2] mm: drop migrate type checks from has_unmovable_pages"
In reply to: Jonathan Cameron: "Re: [PATCH 3/3] iio: adc: stm32: add support for differential channels"
Next in thread: Fabrice Gasnier: "[PATCH 2/3] iio: adc: stm32: remove const channel names definition"
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