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Date: Wed, 8 May 2024 12:40:49 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: David Lechner <dlechner@...libre.com>
CC: Jonathan Cameron <jic23@...nel.org>, Michael Hennerich
<Michael.Hennerich@...log.com>, Nuno Sá
<nuno.sa@...log.com>, Julien Stephan <jstephan@...libre.com>, Esteban Blanc
<eblanc@...libre.com>, <linux-iio@...r.kernel.org>,
<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC 4/4] iio: adc: ad7380: add support for multiple scan
type
On Tue, 7 May 2024 14:02:08 -0500
David Lechner <dlechner@...libre.com> wrote:
> The AD783x chips have a resolution boost feature that allows for 2
> extra bits of resolution. Previously, we had to choose a scan type to
> fit the largest resolution and manipulate the raw data to fit when the
> resolution was lower. This patch adds support for multiple scan types
> for the voltage input channels so that we can support both resolutions
> without having to manipulate the raw data.
>
> Signed-off-by: David Lechner <dlechner@...libre.com>
I'm wondering about the control mechanism. I was thinking we'd poke
the scan type directly but this may well make more sense.
This is relying on _scale change to trigger the change in the scan type.
That may well be sufficient and I've been over thinking this for far too many
years :)
It will get messy though in some cases as the device might have a PGA on the
front end so we will have a trade off between actual scaling control and
resolution related scale changes. We've had a few device where the scale
calculation is already complex and involves various different hardware
controls, but none have affected the storage format like this.
I'll think some more.
> ---
> drivers/iio/adc/ad7380.c | 185 ++++++++++++++++++++++-------------------------
> 1 file changed, 86 insertions(+), 99 deletions(-)
>
> diff --git a/drivers/iio/adc/ad7380.c b/drivers/iio/adc/ad7380.c
> index e240098708e9..ca317e3a72d9 100644
> --- a/drivers/iio/adc/ad7380.c
> +++ b/drivers/iio/adc/ad7380.c
> @@ -89,14 +89,22 @@ struct ad7380_chip_info {
> const struct ad7380_timing_specs *timing_specs;
> };
>
> -/*
> - * realbits/storagebits cannot be dynamically changed, so in order to
> - * support the resolution boost (additional 2 bits of resolution)
> - * we need to set realbits/storagebits to the maximum value i.e :
> - * - realbits = 16 + 2 = 18, and storagebits = 32 for 16-bits chips
> - * - realbits = 14 + 2 = 16, and storagebits = 16 for 14-bits chips
> - * We need to adjust the scale depending on resolution boost status
> - */
> +/** scan type for 14-bit chips with resolution boost enabled. */
> +static const struct iio_scan_type ad7380_scan_type_14_boost = {
> + .sign = 's',
> + .realbits = 16,
> + .storagebits = 16,
> + .endianness = IIO_CPU,
> +};
> +
> +/** scan type for 16-bit chips with resolution boost enabled. */
> +static const struct iio_scan_type ad7380_scan_type_16_boost = {
> + .sign = 's',
> + .realbits = 18,
> + .storagebits = 32,
> + .endianness = IIO_CPU,
> +};
> +
> #define AD7380_CHANNEL(index, bits, diff) { \
> .type = IIO_VOLTAGE, \
> .info_mask_separate = BIT(IIO_CHAN_INFO_RAW) | \
> @@ -113,10 +121,12 @@ struct ad7380_chip_info {
> .scan_index = (index), \
> .scan_type = { \
> .sign = 's', \
> - .realbits = (bits) + 2, \
> - .storagebits = ((bits) + 2 > 16) ? 32 : 16, \
> + .realbits = (bits), \
> + .storagebits = ((bits) > 16) ? 32 : 16, \
> .endianness = IIO_CPU, \
> }, \
> + .ext_scan_type = &ad7380_scan_type_##bits##_boost, \
> + .num_ext_scan_type = 1, \
> }
>
> #define DEFINE_AD7380_2_CHANNEL(name, bits, diff) \
> @@ -376,67 +386,62 @@ static int ad7380_debugfs_reg_access(struct iio_dev *indio_dev, u32 reg,
> unreachable();
> }
>
> -static int ad7380_prepare_spi_xfer(struct ad7380_state *st, struct spi_transfer *xfer)
> +/**
> + * Reads one set of samples from the device. This is a simultaneous sampling
> + * chip, so all channels are always read at the same time.
> + *
> + * On successful return, the raw data is stored in st->scan_data.raw.
> + */
> +static int ad7380_read_one_sample(struct ad7380_state *st,
> + const struct iio_scan_type *scan_type)
> {
> - int bits_per_word;
> -
> - memset(xfer, 0, sizeof(*xfer));
> -
> - xfer->rx_buf = &st->scan_data.raw;
> -
> - if (st->resolution_boost_enable == RESOLUTION_BOOST_ENABLE)
> - bits_per_word = st->chip_info->channels[0].scan_type.realbits;
> - else
> - bits_per_word = st->chip_info->channels[0].scan_type.realbits - 2;
> -
> - xfer->bits_per_word = bits_per_word;
> + struct spi_transfer xfers[2] = {
> + /* toggle CS (no data xfer) to trigger a conversion */
> + {
> + .speed_hz = AD7380_REG_WR_SPEED_HZ,
> + .bits_per_word = scan_type->realbits,
> + .delay = {
> + .value = T_CONVERT_NS,
> + .unit = SPI_DELAY_UNIT_NSECS,
> + },
> + .cs_change = 1,
> + .cs_change_delay = {
> + .value = st->chip_info->timing_specs->t_csh_ns,
> + .unit = SPI_DELAY_UNIT_NSECS,
> + },
> + },
> + {
> + .rx_buf = &st->scan_data.raw,
> + .len = BITS_TO_BYTES(scan_type->storagebits) *
> + (st->chip_info->num_channels - 1),
> + .bits_per_word = scan_type->realbits,
> + },
> + };
>
> - xfer->len = (st->chip_info->num_channels - 1) * BITS_TO_BYTES(bits_per_word);
> + /*
> + * In normal average oversampling we need to wait for multiple conversions to be done
> + */
> + if (st->oversampling_mode == OS_MODE_NORMAL_AVERAGE && st->oversampling_ratio > 1)
> + xfers[0].delay.value = T_CONVERT_NS + 500 * st->oversampling_ratio;
>
> - return bits_per_word;
> + return spi_sync_transfer(st->spi, xfers, ARRAY_SIZE(xfers));
> }
>
> static irqreturn_t ad7380_trigger_handler(int irq, void *p)
> {
> struct iio_poll_func *pf = p;
> struct iio_dev *indio_dev = pf->indio_dev;
> + const struct iio_chan_spec *chan = &indio_dev->channels[0];
> + const struct iio_scan_type *scan_type = iio_get_current_scan_type(
> + indio_dev, chan);
> struct ad7380_state *st = iio_priv(indio_dev);
> - struct spi_transfer xfer;
> - int bits_per_word, realbits, i, ret;
> + int ret;
>
> - realbits = st->chip_info->channels[0].scan_type.realbits;
> - bits_per_word = ad7380_prepare_spi_xfer(st, &xfer);
>
> - ret = spi_sync_transfer(st->spi, &xfer, 1);
> + ret = ad7380_read_one_sample(st, scan_type);
> if (ret)
> goto out;
>
> - /*
> - * If bits_per_word == realbits (resolution boost enabled), we don't
> - * need to manipulate the raw data, otherwise we may need to fix things
> - * up a bit to fit the scan_type specs
> - */
> - if (bits_per_word < realbits) {
> - if (realbits > 16 && bits_per_word <= 16) {
> - /*
> - * Here realbits > 16 so storagebits is 32 and bits_per_word is <= 16
> - * so we need to sign extend u16 to u32 using reverse order to
> - * avoid writing over union data
> - */
> - for (i = st->chip_info->num_channels - 2; i >= 0; i--)
> - st->scan_data.raw.u32[i] = sign_extend32(st->scan_data.raw.u16[i],
> - bits_per_word - 1);
> - } else if (bits_per_word < 16) {
> - /*
> - * Here realbits <= 16 so storagebits is 16.
> - * We only need to sign extend only if bits_per_word is < 16
> - */
> - for (i = 0; i < st->chip_info->num_channels - 1; i++)
> - st->scan_data.raw.u16[i] = sign_extend32(st->scan_data.raw.u16[i],
> - bits_per_word - 1);
> - }
> - }
> -
> iio_push_to_buffers_with_timestamp(indio_dev, &st->scan_data,
> pf->timestamp);
>
> @@ -447,47 +452,21 @@ static irqreturn_t ad7380_trigger_handler(int irq, void *p)
> }
>
> static int ad7380_read_direct(struct ad7380_state *st,
> - struct iio_chan_spec const *chan, int *val)
> + struct iio_chan_spec const *chan,
> + const struct iio_scan_type *scan_type,
> + int *val)
> {
> - struct spi_transfer xfers[2] = {
> - /* toggle CS (no data xfer) to trigger a conversion */
> - {
> - .speed_hz = AD7380_REG_WR_SPEED_HZ,
> - .bits_per_word = chan->scan_type.realbits,
> - .delay = {
> - .value = T_CONVERT_NS,
> - .unit = SPI_DELAY_UNIT_NSECS,
> - },
> - .cs_change = 1,
> - .cs_change_delay = {
> - .value = st->chip_info->timing_specs->t_csh_ns,
> - .unit = SPI_DELAY_UNIT_NSECS,
> - },
> - },
> - /* then read all channels, it will be filled by ad7380_prepare_spi_xfer */
> - {
> - },
> - };
> - int bits_per_word, ret;
> -
> - /*
> - * In normal average oversampling we need to wait for multiple conversions to be done
> - */
> - if (st->oversampling_mode == OS_MODE_NORMAL_AVERAGE && st->oversampling_ratio > 1)
> - xfers[0].delay.value = T_CONVERT_NS + 500 * st->oversampling_ratio;
> -
> - bits_per_word = ad7380_prepare_spi_xfer(st, &xfers[1]);
> + int ret;
>
> - ret = spi_sync_transfer(st->spi, xfers, ARRAY_SIZE(xfers));
> - if (ret < 0)
> + ret = ad7380_read_one_sample(st, scan_type);
> + if (ret)
> return ret;
> -
> - if (bits_per_word > 16)
> + if (scan_type->storagebits > 16)
> *val = sign_extend32(st->scan_data.raw.u32[chan->scan_index],
> - bits_per_word - 1);
> + scan_type->realbits - 1);
> else
> *val = sign_extend32(st->scan_data.raw.u16[chan->scan_index],
> - bits_per_word - 1);
> + scan_type->realbits - 1);
>
> return IIO_VAL_INT;
> }
> @@ -496,18 +475,14 @@ static int ad7380_read_raw(struct iio_dev *indio_dev,
> struct iio_chan_spec const *chan,
> int *val, int *val2, long info)
> {
> + const struct iio_scan_type *scan_type = iio_get_current_scan_type(
> + indio_dev, chan);
> struct ad7380_state *st = iio_priv(indio_dev);
> - int realbits;
> -
> - if (st->resolution_boost_enable == RESOLUTION_BOOST_ENABLE)
> - realbits = chan->scan_type.realbits;
> - else
> - realbits = chan->scan_type.realbits - 2;
>
> switch (info) {
> case IIO_CHAN_INFO_RAW:
> iio_device_claim_direct_scoped(return -EBUSY, indio_dev) {
> - return ad7380_read_direct(st, chan, val);
> + return ad7380_read_direct(st, chan, scan_type, val);
> }
> unreachable();
> case IIO_CHAN_INFO_SCALE:
> @@ -520,7 +495,7 @@ static int ad7380_read_raw(struct iio_dev *indio_dev,
> * According to IIO ABI, offset is applied before scale,
> * so offset is: vcm_mv / scale
> */
> - *val = st->vcm_mv[chan->channel] * (1 << realbits)
> + *val = st->vcm_mv[chan->channel] * (1 << scan_type->realbits)
> / st->vref_mv;
>
> return IIO_VAL_INT;
> @@ -700,6 +675,17 @@ static int ad7380_write_raw(struct iio_dev *indio_dev,
> }
> }
>
> +static const struct iio_scan_type *ad7380_get_current_scan_type(
> + const struct iio_dev *indio_dev, struct iio_chan_spec const *chan)
> +{
> + struct ad7380_state *st = iio_priv(indio_dev);
> +
> + if (st->resolution_boost_enable && chan->num_ext_scan_type)
> + return chan->ext_scan_type;
> +
> + return &chan->scan_type;
> +}
> +
> static ssize_t oversampling_mode_show(struct device *dev,
> struct device_attribute *attr, char *buf)
> {
> @@ -796,6 +782,7 @@ static const struct iio_info ad7380_info = {
> .read_raw = &ad7380_read_raw,
> .read_avail = &ad7380_read_avail,
> .write_raw = &ad7380_write_raw,
> + .get_current_scan_type = &ad7380_get_current_scan_type,
> .debugfs_reg_access = &ad7380_debugfs_reg_access,
> };
>
>
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