On Thu, 14 Mar 2024 12:43:38 -0500 David Lechner <dlechner@xxxxxxxxxxxx> wrote: > This adds support for AD7944 ADCs wired in "3-wire mode". (NOTE: 3-wire > is the datasheet name for this wiring configuration and has nothing to > do with SPI_3WIRE.) > > In the 3-wire mode, the SPI controller CS line can be wired to the CNV > line on the ADC and used to trigger conversions rather that using a > separate GPIO line. > > The turbo/chain mode compatibility check at the end of the probe > function is technically can't be triggered right now but adding it now > anyway so that we don't forget to add it later when support for > daisy-chaining is added. > > Reviewed-by: Nuno Sa <nuno.sa@xxxxxxxxxx> > Signed-off-by: David Lechner <dlechner@xxxxxxxxxxxx> Applied to the togreg-normal branch of iio.git. I'll rebase that on rc1 once available before exposing it to linux-next. Thanks Jonathan > --- > Changes in v2: > - Use default: in case statements. > - Remove redundant else. > - Explain turbo/chain mode check in commit message. > - Link to v1: https://lore.kernel.org/r/20240311-mainline-ad7944-3-wire-mode-v1-1-8e8199efa1f7@xxxxxxxxxxxx > --- > drivers/iio/adc/ad7944.c | 157 +++++++++++++++++++++++++++++++++++++++++------ > 1 file changed, 139 insertions(+), 18 deletions(-) > > diff --git a/drivers/iio/adc/ad7944.c b/drivers/iio/adc/ad7944.c > index adb007cdd287..d5ec6b5a41c7 100644 > --- a/drivers/iio/adc/ad7944.c > +++ b/drivers/iio/adc/ad7944.c > @@ -32,8 +32,25 @@ struct ad7944_timing_spec { > unsigned int turbo_conv_ns; > }; > > +enum ad7944_spi_mode { > + /* datasheet calls this "4-wire mode" */ > + AD7944_SPI_MODE_DEFAULT, > + /* datasheet calls this "3-wire mode" (not related to SPI_3WIRE!) */ > + AD7944_SPI_MODE_SINGLE, > + /* datasheet calls this "chain mode" */ > + AD7944_SPI_MODE_CHAIN, > +}; > + > +/* maps adi,spi-mode property value to enum */ > +static const char * const ad7944_spi_modes[] = { > + [AD7944_SPI_MODE_DEFAULT] = "", > + [AD7944_SPI_MODE_SINGLE] = "single", > + [AD7944_SPI_MODE_CHAIN] = "chain", > +}; > + > struct ad7944_adc { > struct spi_device *spi; > + enum ad7944_spi_mode spi_mode; > /* Chip-specific timing specifications. */ > const struct ad7944_timing_spec *timing_spec; > /* GPIO connected to CNV pin. */ > @@ -58,6 +75,9 @@ struct ad7944_adc { > } sample __aligned(IIO_DMA_MINALIGN); > }; > > +/* quite time before CNV rising edge */ > +#define T_QUIET_NS 20 > + > static const struct ad7944_timing_spec ad7944_timing_spec = { > .conv_ns = 420, > .turbo_conv_ns = 320, > @@ -110,6 +130,65 @@ AD7944_DEFINE_CHIP_INFO(ad7985, ad7944, 16, 0); > /* fully differential */ > AD7944_DEFINE_CHIP_INFO(ad7986, ad7986, 18, 1); > > +/* > + * ad7944_3wire_cs_mode_conversion - Perform a 3-wire CS mode conversion and > + * acquisition > + * @adc: The ADC device structure > + * @chan: The channel specification > + * Return: 0 on success, a negative error code on failure > + * > + * This performs a conversion and reads data when the chip is wired in 3-wire > + * mode with the CNV line on the ADC tied to the CS line on the SPI controller. > + * > + * Upon successful return adc->sample.raw will contain the conversion result. > + */ > +static int ad7944_3wire_cs_mode_conversion(struct ad7944_adc *adc, > + const struct iio_chan_spec *chan) > +{ > + unsigned int t_conv_ns = adc->always_turbo ? adc->timing_spec->turbo_conv_ns > + : adc->timing_spec->conv_ns; > + struct spi_transfer xfers[] = { > + { > + /* > + * NB: can get better performance from some SPI > + * controllers if we use the same bits_per_word > + * in every transfer. > + */ > + .bits_per_word = chan->scan_type.realbits, > + /* > + * CS is tied to CNV and we need a low to high > + * transition to start the conversion, so place CNV > + * low for t_QUIET to prepare for this. > + */ > + .delay = { > + .value = T_QUIET_NS, > + .unit = SPI_DELAY_UNIT_NSECS, > + }, > + > + }, > + { > + .bits_per_word = chan->scan_type.realbits, > + /* > + * CS has to be high for full conversion time to avoid > + * triggering the busy indication. > + */ > + .cs_off = 1, > + .delay = { > + .value = t_conv_ns, > + .unit = SPI_DELAY_UNIT_NSECS, > + }, > + }, > + { > + /* Then we can read the data during the acquisition phase */ > + .rx_buf = &adc->sample.raw, > + .len = BITS_TO_BYTES(chan->scan_type.storagebits), > + .bits_per_word = chan->scan_type.realbits, > + }, > + }; > + > + return spi_sync_transfer(adc->spi, xfers, ARRAY_SIZE(xfers)); > +} > + > /* > * ad7944_4wire_mode_conversion - Perform a 4-wire mode conversion and acquisition > * @adc: The ADC device structure > @@ -167,9 +246,22 @@ static int ad7944_single_conversion(struct ad7944_adc *adc, > { > int ret; > > - ret = ad7944_4wire_mode_conversion(adc, chan); > - if (ret) > - return ret; > + switch (adc->spi_mode) { > + case AD7944_SPI_MODE_DEFAULT: > + ret = ad7944_4wire_mode_conversion(adc, chan); > + if (ret) > + return ret; > + > + break; > + case AD7944_SPI_MODE_SINGLE: > + ret = ad7944_3wire_cs_mode_conversion(adc, chan); > + if (ret) > + return ret; > + > + break; > + default: > + return -EOPNOTSUPP; > + } > > if (chan->scan_type.storagebits > 16) > *val = adc->sample.raw.u32; > @@ -230,9 +322,23 @@ static irqreturn_t ad7944_trigger_handler(int irq, void *p) > struct ad7944_adc *adc = iio_priv(indio_dev); > int ret; > > - ret = ad7944_4wire_mode_conversion(adc, &indio_dev->channels[0]); > - if (ret) > + switch (adc->spi_mode) { > + case AD7944_SPI_MODE_DEFAULT: > + ret = ad7944_4wire_mode_conversion(adc, &indio_dev->channels[0]); > + if (ret) > + goto out; > + > + break; > + case AD7944_SPI_MODE_SINGLE: > + ret = ad7944_3wire_cs_mode_conversion(adc, &indio_dev->channels[0]); > + if (ret) > + goto out; > + > + break; > + default: > + /* not supported */ > goto out; > + } > > iio_push_to_buffers_with_timestamp(indio_dev, &adc->sample.raw, > pf->timestamp); > @@ -260,16 +366,9 @@ static int ad7944_probe(struct spi_device *spi) > struct ad7944_adc *adc; > bool have_refin = false; > struct regulator *ref; > + const char *str_val; > int ret; > > - /* > - * driver currently only supports the conventional "4-wire" mode and > - * not other special wiring configurations. > - */ > - if (device_property_present(dev, "adi,spi-mode")) > - return dev_err_probe(dev, -EINVAL, > - "adi,spi-mode is not currently supported\n"); > - > indio_dev = devm_iio_device_alloc(dev, sizeof(*adc)); > if (!indio_dev) > return -ENOMEM; > @@ -283,6 +382,22 @@ static int ad7944_probe(struct spi_device *spi) > > adc->timing_spec = chip_info->timing_spec; > > + if (device_property_read_string(dev, "adi,spi-mode", &str_val) == 0) { > + ret = sysfs_match_string(ad7944_spi_modes, str_val); > + if (ret < 0) > + return dev_err_probe(dev, -EINVAL, > + "unsupported adi,spi-mode\n"); > + > + adc->spi_mode = ret; > + } else { > + /* absence of adi,spi-mode property means default mode */ > + adc->spi_mode = AD7944_SPI_MODE_DEFAULT; > + } > + > + if (adc->spi_mode == AD7944_SPI_MODE_CHAIN) > + return dev_err_probe(dev, -EINVAL, > + "chain mode is not implemented\n"); > + > /* > * Some chips use unusual word sizes, so check now instead of waiting > * for the first xfer. > @@ -349,15 +464,17 @@ static int ad7944_probe(struct spi_device *spi) > adc->ref_mv = AD7944_INTERNAL_REF_MV; > } > > - /* > - * CNV gpio is required in 4-wire mode which is the only currently > - * supported mode. > - */ > - adc->cnv = devm_gpiod_get(dev, "cnv", GPIOD_OUT_LOW); > + adc->cnv = devm_gpiod_get_optional(dev, "cnv", GPIOD_OUT_LOW); > if (IS_ERR(adc->cnv)) > return dev_err_probe(dev, PTR_ERR(adc->cnv), > "failed to get CNV GPIO\n"); > > + if (!adc->cnv && adc->spi_mode == AD7944_SPI_MODE_DEFAULT) > + return dev_err_probe(&spi->dev, -EINVAL, "CNV GPIO is required\n"); > + if (adc->cnv && adc->spi_mode != AD7944_SPI_MODE_DEFAULT) > + return dev_err_probe(&spi->dev, -EINVAL, > + "CNV GPIO in single and chain mode is not currently supported\n"); > + > adc->turbo = devm_gpiod_get_optional(dev, "turbo", GPIOD_OUT_LOW); > if (IS_ERR(adc->turbo)) > return dev_err_probe(dev, PTR_ERR(adc->turbo), > @@ -369,6 +486,10 @@ static int ad7944_probe(struct spi_device *spi) > return dev_err_probe(dev, -EINVAL, > "cannot have both turbo-gpios and adi,always-turbo\n"); > > + if (adc->spi_mode == AD7944_SPI_MODE_CHAIN && adc->always_turbo) > + return dev_err_probe(dev, -EINVAL, > + "cannot have both chain mode and always turbo\n"); > + > indio_dev->name = chip_info->name; > indio_dev->modes = INDIO_DIRECT_MODE; > indio_dev->info = &ad7944_iio_info; > > --- > base-commit: bbafdb305d6b00934cc09a90ec1bb659d43e5171 > change-id: 20240311-mainline-ad7944-3-wire-mode-c240fe8af979
