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Message-ID: <20240311-mainline-ad7944-3-wire-mode-v1-1-8e8199efa1f7@baylibre.com>
Date: Mon, 11 Mar 2024 16:26:46 -0500
From: David Lechner <dlechner@...libre.com>
To: Jonathan Cameron <jic23@...nel.org>
Cc: David Lechner <dlechner@...libre.com>,
Michael Hennerich <michael.hennerich@...log.com>,
Nuno Sá <nuno.sa@...log.com>,
linux-iio@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: [PATCH] iio: adc: ad7944: Add support for "3-wire mode"
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.
Signed-off-by: David Lechner <dlechner@...libre.com>
---
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..8f466eb66bc4 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;
+ case AD7944_SPI_MODE_CHAIN:
+ 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;
+ case AD7944_SPI_MODE_CHAIN:
+ /* 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");
+ else 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
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