Until now, the conversion were triggered by setting high the GPIO
connected to the convst pin. This commit gives the possibility to
connect the convst pin to a PWM.
Connecting a PWM allows to have a better control on the samplerate,
but it must be handled with care, as it is completely decorrelated of
the driver's busy pin handling.
Hence it is not recommended to be used "as is" but must be exploited
in conjunction with IIO backend, and for now only a mock functionality
is enabled, i.e PWM never swings, but is used as a GPIO, i.e duty_cycle
== period equals high state, duty_cycle == 0 equals low state.

This mock functionality will be disabled after the IIO backend usecase
is introduced.

Signed-off-by: Guillaume Stols <gstols@baylibre.com>
---
 drivers/iio/adc/ad7606.c | 147 ++++++++++++++++++++++++++++++++++++++++++++---
 drivers/iio/adc/ad7606.h |   2 +
 2 files changed, 142 insertions(+), 7 deletions(-)

diff --git a/drivers/iio/adc/ad7606.c b/drivers/iio/adc/ad7606.c
index 71362eafe838..dd4e0c6fce3e 100644
--- a/drivers/iio/adc/ad7606.c
+++ b/drivers/iio/adc/ad7606.c
@@ -13,10 +13,12 @@
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/property.h>
+#include <linux/pwm.h>
 #include <linux/regulator/consumer.h>
 #include <linux/sched.h>
 #include <linux/slab.h>
 #include <linux/sysfs.h>
+#include <linux/units.h>
 #include <linux/util_macros.h>
 
 #include <linux/iio/buffer.h>
@@ -299,6 +301,73 @@ static int ad7606_reg_access(struct iio_dev *indio_dev,
 	}
 }
 
+static int ad7606_pwm_set_high(struct ad7606_state *st)
+{
+	struct pwm_state cnvst_pwm_state;
+	int ret;
+
+	pwm_get_state(st->cnvst_pwm, &cnvst_pwm_state);
+	cnvst_pwm_state.enabled = true;
+	cnvst_pwm_state.duty_cycle = cnvst_pwm_state.period;
+
+	ret = pwm_apply_might_sleep(st->cnvst_pwm, &cnvst_pwm_state);
+	/* sleep 2 µS to let finish the current pulse */
+	fsleep(2);
+
+	return ret;
+}
+
+static int ad7606_pwm_set_low(struct ad7606_state *st)
+{
+	struct pwm_state cnvst_pwm_state;
+	int ret;
+
+	pwm_get_state(st->cnvst_pwm, &cnvst_pwm_state);
+	cnvst_pwm_state.enabled = true;
+	cnvst_pwm_state.duty_cycle = 0;
+
+	ret = pwm_apply_might_sleep(st->cnvst_pwm, &cnvst_pwm_state);
+	/* sleep 2 µS to let finish the current pulse */
+	fsleep(2);
+
+	return ret;
+}
+
+static bool ad7606_pwm_is_swinging(struct ad7606_state *st)
+{
+	struct pwm_state cnvst_pwm_state;
+
+	pwm_get_state(st->cnvst_pwm, &cnvst_pwm_state);
+
+	return cnvst_pwm_state.duty_cycle != cnvst_pwm_state.period &&
+	       cnvst_pwm_state.duty_cycle != 0;
+}
+
+static int ad7606_set_sampling_freq(struct ad7606_state *st, unsigned long freq)
+{
+	struct pwm_state cnvst_pwm_state;
+	bool is_swinging = ad7606_pwm_is_swinging(st);
+	bool is_high;
+
+	if (freq == 0)
+		return -EINVAL;
+
+	/* Retrieve the previous state. */
+	pwm_get_state(st->cnvst_pwm, &cnvst_pwm_state);
+	is_high = cnvst_pwm_state.duty_cycle == cnvst_pwm_state.period;
+
+	cnvst_pwm_state.period = DIV_ROUND_UP_ULL(NSEC_PER_SEC, freq);
+	cnvst_pwm_state.polarity = PWM_POLARITY_NORMAL;
+	if (is_high)
+		cnvst_pwm_state.duty_cycle = cnvst_pwm_state.period;
+	else if (is_swinging)
+		cnvst_pwm_state.duty_cycle = cnvst_pwm_state.period / 2;
+	else
+		cnvst_pwm_state.duty_cycle = 0;
+
+	return pwm_apply_might_sleep(st->cnvst_pwm, &cnvst_pwm_state);
+}
+
 static int ad7606_read_samples(struct ad7606_state *st)
 {
 	unsigned int num = st->chip_info->num_channels - 1;
@@ -324,7 +393,13 @@ static irqreturn_t ad7606_trigger_handler(int irq, void *p)
 error_ret:
 	iio_trigger_notify_done(indio_dev->trig);
 	/* The rising edge of the CONVST signal starts a new conversion. */
-	gpiod_set_value(st->gpio_convst, 1);
+	if (st->gpio_convst) {
+		gpiod_set_value(st->gpio_convst, 1);
+	} else {
+		ret = ad7606_pwm_set_high(st)
+		if (ret < 0)
+			dev_err(st->dev, "Could not set PWM to high.");
+	}
 
 	return IRQ_HANDLED;
 }
@@ -337,7 +412,13 @@ static int ad7606_scan_direct(struct iio_dev *indio_dev, unsigned int ch,
 	const struct iio_chan_spec *chan;
 	int ret;
 
-	gpiod_set_value(st->gpio_convst, 1);
+	if (st->gpio_convst) {
+		gpiod_set_value(st->gpio_convst, 1);
+	} else {
+		ret = ad7606_pwm_set_high(st);
+		if (ret < 0)
+			return ret;
+	}
 	ret = wait_for_completion_timeout(&st->completion,
 					  msecs_to_jiffies(1000));
 	if (!ret) {
@@ -363,6 +444,11 @@ static int ad7606_scan_direct(struct iio_dev *indio_dev, unsigned int ch,
 	}
 
 error_ret:
+	if (!st->gpio_convst) {
+		ret = ad7606_pwm_set_low(st);
+		if (ret < 0)
+			return ret;
+	}
 	gpiod_set_value(st->gpio_convst, 0);
 
 	return ret;
@@ -662,8 +748,9 @@ static int ad7606_request_gpios(struct ad7606_state *st)
 {
 	struct device *dev = st->dev;
 
-	st->gpio_convst = devm_gpiod_get(dev, "adi,conversion-start",
-					 GPIOD_OUT_LOW);
+	st->gpio_convst = devm_gpiod_get_optional(dev, "adi,conversion-start",
+						  GPIOD_OUT_LOW);
+
 	if (IS_ERR(st->gpio_convst))
 		return PTR_ERR(st->gpio_convst);
 
@@ -705,14 +792,24 @@ static irqreturn_t ad7606_interrupt(int irq, void *dev_id)
 {
 	struct iio_dev *indio_dev = dev_id;
 	struct ad7606_state *st = iio_priv(indio_dev);
+	int ret;
 
 	if (iio_buffer_enabled(indio_dev)) {
-		gpiod_set_value(st->gpio_convst, 0);
+		if (st->gpio_convst) {
+			gpiod_set_value(st->gpio_convst, 0);
+		} else {
+			ret = ad7606_pwm_set_low(st);
+			if (ret < 0) {
+				dev_err(st->dev, "PWM set low failed");
+				goto done;
+			}
+		}
 		iio_trigger_poll_nested(st->trig);
 	} else {
 		complete(&st->completion);
 	}
 
+done:
 	return IRQ_HANDLED;
 };
 
@@ -731,7 +828,10 @@ static int ad7606_buffer_postenable(struct iio_dev *indio_dev)
 {
 	struct ad7606_state *st = iio_priv(indio_dev);
 
-	gpiod_set_value(st->gpio_convst, 1);
+	if (st->gpio_convst)
+		gpiod_set_value(st->gpio_convst, 1);
+	else
+		return ad7606_pwm_set_high(st);
 
 	return 0;
 }
@@ -740,7 +840,10 @@ static int ad7606_buffer_predisable(struct iio_dev *indio_dev)
 {
 	struct ad7606_state *st = iio_priv(indio_dev);
 
-	gpiod_set_value(st->gpio_convst, 0);
+	if (st->gpio_convst)
+		gpiod_set_value(st->gpio_convst, 0);
+	else
+		return ad7606_pwm_set_low(st);
 
 	return 0;
 }
@@ -874,6 +977,11 @@ static int ad7606_chan_scales_setup(struct iio_dev *indio_dev)
 	return 0;
 }
 
+static void ad7606_pwm_disable(void *data)
+{
+	pwm_disable(data);
+}
+
 int ad7606_probe(struct device *dev, int irq, void __iomem *base_address,
 		 const char *name, unsigned int id,
 		 const struct ad7606_bus_ops *bops)
@@ -950,6 +1058,31 @@ int ad7606_probe(struct device *dev, int irq, void __iomem *base_address,
 	if (ret)
 		return ret;
 
+	/* If convst pin is not defined, setup PWM. */
+	if (!st->gpio_convst) {
+		st->cnvst_pwm = devm_pwm_get(dev, NULL);
+		if (IS_ERR(st->cnvst_pwm))
+			return PTR_ERR(st->cnvst_pwm);
+
+		/* The PWM is initialized at 1MHz to have a fast enough GPIO emulation. */
+		ret = ad7606_set_sampling_freq(st, 1 * MEGA);
+		if (ret)
+			return ret;
+
+		ret = ad7606_pwm_set_low(st);
+		if (ret)
+			return ret;
+
+		/*
+		 * PWM is not disabled when sampling stops, but instead its duty cycle is set
+		 * to 0% to be sure we have a "low" state. After we unload the driver, let's
+		 * disable the PWM.
+		 */
+		ret = devm_add_action_or_reset(dev, ad7606_pwm_disable,
+					       st->cnvst_pwm);
+		if (ret)
+			return ret;
+	}
 	st->trig = devm_iio_trigger_alloc(dev, "%s-dev%d",
 					  indio_dev->name,
 					  iio_device_id(indio_dev));
diff --git a/drivers/iio/adc/ad7606.h b/drivers/iio/adc/ad7606.h
index fc05a4afa3b8..760cf5e2ecb6 100644
--- a/drivers/iio/adc/ad7606.h
+++ b/drivers/iio/adc/ad7606.h
@@ -115,6 +115,7 @@ struct ad7606_chan_scale {
  * @bops		bus operations (SPI or parallel)
  * @chan_scales		scale configuration for channels
  * @oversampling	oversampling selection
+ * @cnvst_pwm		pointer to the PWM device connected to the cnvst pin
  * @base_address	address from where to read data in parallel operation
  * @sw_mode_en		software mode enabled
  * @oversampling_avail	pointer to the array which stores the available
@@ -142,6 +143,7 @@ struct ad7606_state {
 	const struct ad7606_bus_ops	*bops;
 	struct ad7606_chan_scale	chan_scales[AD760X_MAX_CHANNELS];
 	unsigned int			oversampling;
+	struct pwm_device		*cnvst_pwm;
 	void __iomem			*base_address;
 	bool				sw_mode_en;
 	const unsigned int		*oversampling_avail;

-- 
2.34.1

On Tue, 15 Oct 2024 13:56:17 +0000
Guillaume Stols <gstols@baylibre.com> wrote:

> Until now, the conversion were triggered by setting high the GPIO
> connected to the convst pin. This commit gives the possibility to
> connect the convst pin to a PWM.
> Connecting a PWM allows to have a better control on the samplerate,
> but it must be handled with care, as it is completely decorrelated of
> the driver's busy pin handling.
> Hence it is not recommended to be used "as is" but must be exploited
> in conjunction with IIO backend, and for now only a mock functionality
> is enabled, i.e PWM never swings, but is used as a GPIO, i.e duty_cycle
> == period equals high state, duty_cycle == 0 equals low state.
> 
> This mock functionality will be disabled after the IIO backend usecase
> is introduced.
> 
> Signed-off-by: Guillaume Stols <gstols@baylibre.com>
Trivial fix needed so this builds.

>  static int ad7606_read_samples(struct ad7606_state *st)
>  {
>  	unsigned int num = st->chip_info->num_channels - 1;
> @@ -324,7 +393,13 @@ static irqreturn_t ad7606_trigger_handler(int irq, void *p)
>  error_ret:
>  	iio_trigger_notify_done(indio_dev->trig);
>  	/* The rising edge of the CONVST signal starts a new conversion. */
> -	gpiod_set_value(st->gpio_convst, 1);
> +	if (st->gpio_convst) {
> +		gpiod_set_value(st->gpio_convst, 1);
> +	} else {
> +		ret = ad7606_pwm_set_high(st)
Missing ;

> +		if (ret < 0)
> +			dev_err(st->dev, "Could not set PWM to high.");
> +	}