Re: [PATCH 3/3] iio: adc: stm32: add optional min-sample-time

From: Fabrice Gasnier
Date: Mon Jul 24 2017 - 04:17:08 EST

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On 07/23/2017 01:00 PM, Jonathan Cameron wrote:
> On Tue, 18 Jul 2017 14:35:32 +0200
> Fabrice Gasnier <fabrice.gasnier@xxxxxx> wrote:
>
>> STM32 ADC allows each channel to be sampled with a different sampling time,
>> by setting SMPR registers. Basically, value depends on local electrical
>> properties. Selecting correct value for sampling time highly depends on
>> analog source impedance. There is a manual that may help in this process:
>> 'How to get the best ADC accuracy in STM32...'
>>
>> This patch allows to configure min-sample-time via device tree, either for:
>> - all channels at once:
>> min-sample-time = <10000>; /* nanosecs */
>>
>> - independently for each channel (must match "st,adc-channels" list):
>> st,adc-channels = <0 1>;
>> min-sample-time = <5000 10000>; /* nanosecs */
>>
>> Signed-off-by: Fabrice Gasnier <fabrice.gasnier@xxxxxx>
>
> On question inline which may well just be down to me missing what
> happens when you query index element 2 from a 1 element device tree
> array.

Hi Jonathan,

I should probably comment on it, please see inline.

>> ---
>> drivers/iio/adc/stm32-adc.c | 134 ++++++++++++++++++++++++++++++++++++++++++--
>> 1 file changed, 130 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/iio/adc/stm32-adc.c b/drivers/iio/adc/stm32-adc.c
>> index 5bfcc1f..e6f6b5e 100644
>> --- a/drivers/iio/adc/stm32-adc.c
>> +++ b/drivers/iio/adc/stm32-adc.c
>> @@ -83,6 +83,8 @@
>> #define STM32H7_ADC_IER 0x04
>> #define STM32H7_ADC_CR 0x08
>> #define STM32H7_ADC_CFGR 0x0C
>> +#define STM32H7_ADC_SMPR1 0x14
>> +#define STM32H7_ADC_SMPR2 0x18
>> #define STM32H7_ADC_PCSEL 0x1C
>> #define STM32H7_ADC_SQR1 0x30
>> #define STM32H7_ADC_SQR2 0x34
>> @@ -151,6 +153,7 @@ enum stm32h7_adc_dmngt {
>> #define STM32H7_BOOST_CLKRATE 20000000UL
>>
>> #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
>> #define STM32_ADC_TIMEOUT (msecs_to_jiffies(STM32_ADC_TIMEOUT_US / 1000))
>>
>> @@ -227,6 +230,8 @@ struct stm32_adc_regs {
>> * @exten: trigger control register & bitfield
>> * @extsel: trigger selection register & bitfield
>> * @res: resolution selection register & bitfield
>> + * @smpr: smpr1 & smpr2 registers offset array
>> + * @smp_bits: smpr1 & smpr2 index and bitfields
>> */
>> struct stm32_adc_regspec {
>> const u32 dr;
>> @@ -236,6 +241,8 @@ struct stm32_adc_regspec {
>> const struct stm32_adc_regs exten;
>> const struct stm32_adc_regs extsel;
>> const struct stm32_adc_regs res;
>> + const u32 smpr[2];
>> + const struct stm32_adc_regs *smp_bits;
>> };
>>
>> struct stm32_adc;
>> @@ -251,6 +258,7 @@ struct stm32_adc_regspec {
>> * @start_conv: routine to start conversions
>> * @stop_conv: routine to stop conversions
>> * @unprepare: optional unprepare routine (disable, power-down)
>> + * @smp_cycles: programmable sampling time (ADC clock cycles)
>> */
>> struct stm32_adc_cfg {
>> const struct stm32_adc_regspec *regs;
>> @@ -262,6 +270,7 @@ struct stm32_adc_cfg {
>> void (*start_conv)(struct stm32_adc *, bool dma);
>> void (*stop_conv)(struct stm32_adc *);
>> void (*unprepare)(struct stm32_adc *);
>> + const unsigned int *smp_cycles;
>> };
>>
>> /**
>> @@ -283,6 +292,7 @@ struct stm32_adc_cfg {
>> * @rx_dma_buf: dma rx buffer bus address
>> * @rx_buf_sz: dma rx buffer size
>> * @pcsel bitmask to preselect channels on some devices
>> + * @smpr_val: sampling time settings (e.g. smpr1 / smpr2)
>> * @cal: optional calibration data on some devices
>> */
>> struct stm32_adc {
>> @@ -303,6 +313,7 @@ struct stm32_adc {
>> dma_addr_t rx_dma_buf;
>> unsigned int rx_buf_sz;
>> u32 pcsel;
>> + u32 smpr_val[2];
>> struct stm32_adc_calib cal;
>> };
>>
>> @@ -431,6 +442,39 @@ struct stm32_adc_info {
>> {}, /* sentinel */
>> };
>>
>> +/**
>> + * stm32f4_smp_bits[] - describe sampling time register index & bit fields
>> + * Sorted so it can be indexed by channel number.
>> + */
>> +static const struct stm32_adc_regs stm32f4_smp_bits[] = {
>> + /* STM32F4_ADC_SMPR2: smpr[] index, mask, shift for SMP0 to SMP9 */
>> + { 1, GENMASK(2, 0), 0 },
>> + { 1, GENMASK(5, 3), 3 },
>> + { 1, GENMASK(8, 6), 6 },
>> + { 1, GENMASK(11, 9), 9 },
>> + { 1, GENMASK(14, 12), 12 },
>> + { 1, GENMASK(17, 15), 15 },
>> + { 1, GENMASK(20, 18), 18 },
>> + { 1, GENMASK(23, 21), 21 },
>> + { 1, GENMASK(26, 24), 24 },
>> + { 1, GENMASK(29, 27), 27 },
>> + /* STM32F4_ADC_SMPR1, smpr[] index, mask, shift for SMP10 to SMP18 */
>> + { 0, GENMASK(2, 0), 0 },
>> + { 0, GENMASK(5, 3), 3 },
>> + { 0, GENMASK(8, 6), 6 },
>> + { 0, GENMASK(11, 9), 9 },
>> + { 0, GENMASK(14, 12), 12 },
>> + { 0, GENMASK(17, 15), 15 },
>> + { 0, GENMASK(20, 18), 18 },
>> + { 0, GENMASK(23, 21), 21 },
>> + { 0, GENMASK(26, 24), 24 },
>> +};
>> +
>> +/* STM32F4 programmable sampling time (ADC clock cycles) */
>> +static const unsigned int stm32f4_adc_smp_cycles[STM32_ADC_MAX_SMP + 1] = {
>> + 3, 15, 28, 56, 84, 112, 144, 480,
>> +};
>> +
>> static const struct stm32_adc_regspec stm32f4_adc_regspec = {
>> .dr = STM32F4_ADC_DR,
>> .ier_eoc = { STM32F4_ADC_CR1, STM32F4_EOCIE },
>> @@ -440,6 +484,8 @@ struct stm32_adc_info {
>> .extsel = { STM32F4_ADC_CR2, STM32F4_EXTSEL_MASK,
>> STM32F4_EXTSEL_SHIFT },
>> .res = { STM32F4_ADC_CR1, STM32F4_RES_MASK, STM32F4_RES_SHIFT },
>> + .smpr = { STM32F4_ADC_SMPR1, STM32F4_ADC_SMPR2 },
>> + .smp_bits = stm32f4_smp_bits,
>> };
>>
>> static const struct stm32_adc_regs stm32h7_sq[STM32_ADC_MAX_SQ + 1] = {
>> @@ -483,6 +529,40 @@ struct stm32_adc_info {
>> {},
>> };
>>
>> +/**
>> + * stm32h7_smp_bits - describe sampling time register index & bit fields
>> + * Sorted so it can be indexed by channel number.
>> + */
>> +static const struct stm32_adc_regs stm32h7_smp_bits[] = {
>> + /* STM32H7_ADC_SMPR1, smpr[] index, mask, shift for SMP0 to SMP9 */
>> + { 0, GENMASK(2, 0), 0 },
>> + { 0, GENMASK(5, 3), 3 },
>> + { 0, GENMASK(8, 6), 6 },
>> + { 0, GENMASK(11, 9), 9 },
>> + { 0, GENMASK(14, 12), 12 },
>> + { 0, GENMASK(17, 15), 15 },
>> + { 0, GENMASK(20, 18), 18 },
>> + { 0, GENMASK(23, 21), 21 },
>> + { 0, GENMASK(26, 24), 24 },
>> + { 0, GENMASK(29, 27), 27 },
>> + /* STM32H7_ADC_SMPR2, smpr[] index, mask, shift for SMP10 to SMP19 */
>> + { 1, GENMASK(2, 0), 0 },
>> + { 1, GENMASK(5, 3), 3 },
>> + { 1, GENMASK(8, 6), 6 },
>> + { 1, GENMASK(11, 9), 9 },
>> + { 1, GENMASK(14, 12), 12 },
>> + { 1, GENMASK(17, 15), 15 },
>> + { 1, GENMASK(20, 18), 18 },
>> + { 1, GENMASK(23, 21), 21 },
>> + { 1, GENMASK(26, 24), 24 },
>> + { 1, GENMASK(29, 27), 27 },
>> +};
>> +
>> +/* STM32H7 programmable sampling time (ADC clock cycles, rounded down) */
>> +static const unsigned int stm32h7_adc_smp_cycles[STM32_ADC_MAX_SMP + 1] = {
>> + 1, 2, 8, 16, 32, 64, 387, 810,
>> +};
>> +
>> static const struct stm32_adc_regspec stm32h7_adc_regspec = {
>> .dr = STM32H7_ADC_DR,
>> .ier_eoc = { STM32H7_ADC_IER, STM32H7_EOCIE },
>> @@ -492,6 +572,8 @@ struct stm32_adc_info {
>> .extsel = { STM32H7_ADC_CFGR, STM32H7_EXTSEL_MASK,
>> STM32H7_EXTSEL_SHIFT },
>> .res = { STM32H7_ADC_CFGR, STM32H7_RES_MASK, STM32H7_RES_SHIFT },
>> + .smpr = { STM32H7_ADC_SMPR1, STM32H7_ADC_SMPR2 },
>> + .smp_bits = stm32h7_smp_bits,
>> };
>>
>> /**
>> @@ -933,6 +1015,7 @@ static void stm32h7_adc_unprepare(struct stm32_adc *adc)
>> * @scan_mask: channels to be converted
>> *
>> * Conversion sequence :
>> + * Apply sampling time settings for all channels.
>> * Configure ADC scan sequence based on selected channels in scan_mask.
>> * Add channels to SQR registers, from scan_mask LSB to MSB, then
>> * program sequence len.
>> @@ -946,6 +1029,10 @@ static int stm32_adc_conf_scan_seq(struct iio_dev *indio_dev,
>> u32 val, bit;
>> int i = 0;
>>
>> + /* Apply sampling time settings */
>> + stm32_adc_writel(adc, adc->cfg->regs->smpr[0], adc->smpr_val[0]);
>> + stm32_adc_writel(adc, adc->cfg->regs->smpr[1], adc->smpr_val[1]);
>> +
>> for_each_set_bit(bit, scan_mask, indio_dev->masklength) {
>> chan = indio_dev->channels + bit;
>> /*
>> @@ -1079,6 +1166,7 @@ static int stm32_adc_get_trig_pol(struct iio_dev *indio_dev,
>> * @res: conversion result
>> *
>> * The function performs a single conversion on a given channel:
>> + * - Apply sampling time settings
>> * - Program sequencer with one channel (e.g. in SQ1 with len = 1)
>> * - Use SW trigger
>> * - Start conversion, then wait for interrupt completion.
>> @@ -1103,6 +1191,10 @@ static int stm32_adc_single_conv(struct iio_dev *indio_dev,
>> return ret;
>> }
>>
>> + /* Apply sampling time settings */
>> + stm32_adc_writel(adc, regs->smpr[0], adc->smpr_val[0]);
>> + stm32_adc_writel(adc, regs->smpr[1], adc->smpr_val[1]);
>> +
>> /* Program chan number in regular sequence (SQ1) */
>> val = stm32_adc_readl(adc, regs->sqr[1].reg);
>> val &= ~regs->sqr[1].mask;
>> @@ -1507,10 +1599,28 @@ static int stm32_adc_of_get_resolution(struct iio_dev *indio_dev)
>> return 0;
>> }
>>
>> +static void stm32_adc_smpr_init(struct stm32_adc *adc, int channel, u32 smp_ns)
>> +{
>> + const struct stm32_adc_regs *smpr = &adc->cfg->regs->smp_bits[channel];
>> + u32 period_ns, shift = smpr->shift, mask = smpr->mask;
>> + unsigned int smp, r = smpr->reg;
>> +
>> + /* Determine sampling time (ADC clock cycles) */
>> + period_ns = NSEC_PER_SEC / adc->common->rate;
>> + for (smp = 0; smp <= STM32_ADC_MAX_SMP; smp++)
>> + if ((period_ns * adc->cfg->smp_cycles[smp]) >= smp_ns)
>> + break;
>> + if (smp > STM32_ADC_MAX_SMP)
>> + smp = STM32_ADC_MAX_SMP;
>> +
>> + /* pre-build sampling time registers (e.g. smpr1, smpr2) */
>> + adc->smpr_val[r] = (adc->smpr_val[r] & ~mask) | (smp << shift);
>> +}
>> +
>> static void stm32_adc_chan_init_one(struct iio_dev *indio_dev,
>> struct iio_chan_spec *chan,
>> const struct stm32_adc_chan_spec *channel,
>> - int scan_index)
>> + int scan_index, u32 smp)
>> {
>> struct stm32_adc *adc = iio_priv(indio_dev);
>>
>> @@ -1526,6 +1636,9 @@ static void stm32_adc_chan_init_one(struct iio_dev *indio_dev,
>> 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);
>> }
>> @@ -1538,8 +1651,8 @@ static int stm32_adc_chan_of_init(struct iio_dev *indio_dev)
>> struct property *prop;
>> const __be32 *cur;
>> struct iio_chan_spec *channels;
>> - int scan_index = 0, num_channels;
>> - u32 val;
>> + int scan_index = 0, num_channels, ret;
>> + u32 val, smp = 0;
>>
>> num_channels = of_property_count_u32_elems(node, "st,adc-channels");
>> if (num_channels < 0 ||
>> @@ -1548,6 +1661,13 @@ static int stm32_adc_chan_of_init(struct iio_dev *indio_dev)
>> return num_channels < 0 ? num_channels : -EINVAL;
>> }
>>
>> + /* Optional sample time is provided either for each, or all channels */
>> + ret = of_property_count_u32_elems(node, "min-sample-time");
>> + if (ret > 1 && ret != num_channels) {
>> + dev_err(&indio_dev->dev, "Invalid min-sample-time\n");
>> + return -EINVAL;
>> + }
>> +
>> channels = devm_kcalloc(&indio_dev->dev, num_channels,
>> sizeof(struct iio_chan_spec), GFP_KERNEL);
>> if (!channels)
>> @@ -1558,9 +1678,13 @@ static int stm32_adc_chan_of_init(struct iio_dev *indio_dev)
>> dev_err(&indio_dev->dev, "Invalid channel %d\n", val);
>> return -EINVAL;
>> }
>> +
>> + of_property_read_u32_index(node, "min-sample-time", scan_index,
>> + &smp);
>> +
> I might be missing something, but doesn't this fail for the single shared
> value case?

Yes, this fails in the single shared value case, with index >= 1.
Rewinding... when index is 0, it picks up 1st (shared) value.
Then fails for other index values.

of_property_read_u32_index() documentation states out value remains
untouched in case of error:
/**
* of_property_read_u32_index...
[...]
* The out_value is modified only if a valid u32 value can be decoded.

This is what I use here (as far as I tested it, it worked like a charm).
Do you wish I add a comment to describe this ?

Please let me know,
Best Regards,
Fabrice

>> stm32_adc_chan_init_one(indio_dev, &channels[scan_index],
>> &adc_info->channels[val],
>> - scan_index);
>> + scan_index, smp);
>> scan_index++;
>> }
>>
>> @@ -1755,6 +1879,7 @@ static int stm32_adc_remove(struct platform_device *pdev)
>> .clk_required = true,
>> .start_conv = stm32f4_adc_start_conv,
>> .stop_conv = stm32f4_adc_stop_conv,
>> + .smp_cycles = stm32f4_adc_smp_cycles,
>> };
>>
>> static const struct stm32_adc_cfg stm32h7_adc_cfg = {
>> @@ -1766,6 +1891,7 @@ static int stm32_adc_remove(struct platform_device *pdev)
>> .stop_conv = stm32h7_adc_stop_conv,
>> .prepare = stm32h7_adc_prepare,
>> .unprepare = stm32h7_adc_unprepare,
>> + .smp_cycles = stm32h7_adc_smp_cycles,
>> };
>>
>> static const struct of_device_id stm32_adc_of_match[] = {
>

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