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

Jonathan Cameron
2017-07-23T11:00:30Z

On Tue, 18 Jul 2017 14:35:32 +0200
Fabrice Gasnier <fabrice.gasnier@st.com> 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@st.com>

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.
> ---
> 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?
> 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[] = {