iio: adc: ad7476: Support ROHM BD79105

The ROHM BD79105 is a simple 16-bit ADC accessible via SPI*.

The BD79105 has a CONVSTART pin, which must be set high to start the ADC
conversion. Unlike with the ad7091 and ad7091r which also have a
CONVSTART pin, the BD79105 requires that the pin must remain high also
for the duration of the SPI access.

(*) Couple of words about the SPI. The BD79105 has pins named as
CONVSTART, SCLK, DIN and DOUT. For the curious reader, DIN is not SPI
ISO.

DIN is a signal which can be used as a chip-select. When DIN is pulled
low, the ADC will output the completed measurement via DOUT as SCLK is
clocked. According to the data-sheet, the DIN can also be used for
daisy-chaining multiple ADCs. Furthermore, DOUT can be used also for a
'data-ready' -IRQ. These modes aren't supported by this driver.

Support reading ADC scale and data from the BD79105 using SPI, when DIN
is used as a chip-select.

Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Reviewed-by: Andy Shevchenko <andy@kernel.org>
Link: https://patch.msgid.link/6ee06d551256db9213ccbe72f44cfe9452717716.1754901948.git.mazziesaccount@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

1 files changed, 39 insertions, 0 deletions

diff --git a/drivers/iio/adc/ad7476.c b/drivers/iio/adc/ad7476.c
index 6cb2cbeafbd3..1bec6657394c 100644
--- a/drivers/iio/adc/ad7476.c
+++ b/drivers/iio/adc/ad7476.c
@@ -32,8 +32,10 @@ struct ad7476_chip_info {
 	struct iio_chan_spec		channel[2];
 	void (*reset)(struct ad7476_state *);
 	void (*conversion_pre_op)(struct ad7476_state *st);
+	void (*conversion_post_op)(struct ad7476_state *st);
 	bool				has_vref;
 	bool				has_vdrive;
+	bool				convstart_required;
 };
 
 struct ad7476_state {
@@ -64,6 +66,18 @@ static void ad7091_convst(struct ad7476_state *st)
 	udelay(1); /* Conversion time: 650 ns max */
 }
 
+static void bd79105_convst_disable(struct ad7476_state *st)
+{
+	gpiod_set_value_cansleep(st->convst_gpio, 0);
+}
+
+static void bd79105_convst_enable(struct ad7476_state *st)
+{
+	gpiod_set_value_cansleep(st->convst_gpio, 1);
+	/* Worst case, 2790 ns required for conversion */
+	ndelay(2790);
+}
+
 static irqreturn_t ad7476_trigger_handler(int irq, void  *p)
 {
 	struct iio_poll_func *pf = p;
@@ -81,6 +95,8 @@ static irqreturn_t ad7476_trigger_handler(int irq, void  *p)
 	iio_push_to_buffers_with_ts(indio_dev, st->data, sizeof(st->data),
 				    iio_get_time_ns(indio_dev));
 done:
+	if (st->chip_info->conversion_post_op)
+		st->chip_info->conversion_post_op(st);
 	iio_trigger_notify_done(indio_dev->trig);
 
 	return IRQ_HANDLED;
@@ -103,6 +119,9 @@ static int ad7476_scan_direct(struct ad7476_state *st)
 	if (ret)
 		return ret;
 
+	if (st->chip_info->conversion_post_op)
+		st->chip_info->conversion_post_op(st);
+
 	return be16_to_cpup((__be16 *)st->data);
 }
 
@@ -273,6 +292,22 @@ static const struct ad7476_chip_info ltc2314_14_chip_info = {
 	.has_vref = true,
 };
 
+static const struct ad7476_chip_info bd79105_chip_info = {
+	.channel[0] = AD7091R_CHAN(16),
+	.channel[1] = IIO_CHAN_SOFT_TIMESTAMP(1),
+	/*
+	 * The BD79105 starts ADC data conversion when the CONVSTART line is
+	 * set HIGH. The CONVSTART must be kept HIGH until the data has been
+	 * read from the ADC.
+	 */
+	.conversion_pre_op = bd79105_convst_enable,
+	.conversion_post_op = bd79105_convst_disable,
+	/* BD79105 won't do conversion without convstart */
+	.convstart_required = true,
+	.has_vref = true,
+	.has_vdrive = true,
+};
+
 static const struct iio_info ad7476_info = {
 	.read_raw = &ad7476_read_raw,
 };
@@ -332,6 +367,9 @@ static int ad7476_probe(struct spi_device *spi)
 	if (IS_ERR(st->convst_gpio))
 		return PTR_ERR(st->convst_gpio);
 
+	if (st->chip_info->convstart_required && !st->convst_gpio)
+		return dev_err_probe(&spi->dev, -EINVAL, "No convstart GPIO\n");
+
 	/*
 	 * This will never happen. Unless someone changes the channel specs
 	 * in this driver. And if someone does, without changing the loop
@@ -401,6 +439,7 @@ static const struct spi_device_id ad7476_id[] = {
 	{ "ads7866", (kernel_ulong_t)&ads7866_chip_info },
 	{ "ads7867", (kernel_ulong_t)&ads7867_chip_info },
 	{ "ads7868", (kernel_ulong_t)&ads7868_chip_info },
+	{ "bd79105", (kernel_ulong_t)&bd79105_chip_info },
 	/*
 	 * The ROHM BU79100G is identical to the TI's ADS7866 from the software
 	 * point of view. The binding document mandates the ADS7866 to be