[PATCH v2] iio: adc: add buffering support to the TI LMP92064 ADC driver

[Leonard Göhrs]

Enable buffered reading of samples from the LMP92064 ADC.
The main benefit of this change is being able to read out current and
voltage measurements in a single transfer, allowing instantaneous power
measurements.

Reads into the buffer can be triggered by any software triggers, e.g.
the iio-trig-hrtimer:

    $ mkdir /sys/kernel/config/iio/triggers/hrtimer/my-trigger
    $ cat /sys/bus/iio/devices/iio\:device3/name
    lmp92064
    $ iio_readdev -t my-trigger -b 16 iio:device3 | hexdump
    WARNING: High-speed mode not enabled
    0000000 0000 0176 0101 0001 5507 abd5 7645 1768
    0000010 0000 016d 0101 0001 ee1e ac6b 7645 1768
    ...

Signed-off-by: Leonard Göhrs <l.goehrs@xxxxxxxxxxxxxx>
---
Changes v1->v2:

  - Remove superfluous .shift = 0 initialization in scan_type.
  - Replace kmalloc buffer allocation for every read with a stack
    allocated structure.
    A struct is used to ensure correct alignment of the timestamp field.
    See e.g. adc/rockchip_saradc.c for other users of the same pattern.
  - Use available_scan_masks and always push both voltage and current
    measurements to the buffer.

---
 drivers/iio/adc/ti-lmp92064.c | 50 +++++++++++++++++++++++++++++++++++
 1 file changed, 50 insertions(+)

diff --git a/drivers/iio/adc/ti-lmp92064.c b/drivers/iio/adc/ti-lmp92064.c
index c30ed824924f3..a4e64ee8a7b50 100644
--- a/drivers/iio/adc/ti-lmp92064.c
+++ b/drivers/iio/adc/ti-lmp92064.c
@@ -16,7 +16,10 @@
 #include <linux/spi/spi.h>
 
 #include <linux/iio/iio.h>
+#include <linux/iio/buffer.h>
 #include <linux/iio/driver.h>
+#include <linux/iio/triggered_buffer.h>
+#include <linux/iio/trigger_consumer.h>
 
 #define TI_LMP92064_REG_CONFIG_A 0x0000
 #define TI_LMP92064_REG_CONFIG_B 0x0001
@@ -91,6 +94,12 @@ static const struct iio_chan_spec lmp92064_adc_channels[] = {
 		.address = TI_LMP92064_CHAN_INC,
 		.info_mask_separate =
 			BIT(IIO_CHAN_INFO_RAW) | BIT(IIO_CHAN_INFO_SCALE),
+		.scan_index = TI_LMP92064_CHAN_INC,
+		.scan_type = {
+			.sign = 'u',
+			.realbits = 12,
+			.storagebits = 16,
+		},
 		.datasheet_name = "INC",
 	},
 	{
@@ -98,8 +107,20 @@ static const struct iio_chan_spec lmp92064_adc_channels[] = {
 		.address = TI_LMP92064_CHAN_INV,
 		.info_mask_separate =
 			BIT(IIO_CHAN_INFO_RAW) | BIT(IIO_CHAN_INFO_SCALE),
+		.scan_index = TI_LMP92064_CHAN_INV,
+		.scan_type = {
+			.sign = 'u',
+			.realbits = 12,
+			.storagebits = 16,
+		},
 		.datasheet_name = "INV",
 	},
+	IIO_CHAN_SOFT_TIMESTAMP(2),
+};
+
+static const unsigned long lmp92064_scan_masks[] = {
+	BIT(TI_LMP92064_CHAN_INC) | BIT(TI_LMP92064_CHAN_INV),
+	0
 };
 
 static int lmp92064_read_meas(struct lmp92064_adc_priv *priv, u16 *res)
@@ -171,6 +192,29 @@ static int lmp92064_read_raw(struct iio_dev *indio_dev,
 	}
 }
 
+static irqreturn_t lmp92064_trigger_handler(int irq, void *p)
+{
+	struct iio_poll_func *pf = p;
+	struct iio_dev *indio_dev = pf->indio_dev;
+	struct lmp92064_adc_priv *priv = iio_priv(indio_dev);
+	struct {
+		u16 values[2];
+		int64_t timestamp;
+	} data;
+	int ret;
+
+	ret = lmp92064_read_meas(priv, data.values);
+	if (ret >= 0) {
+		/* Only push values if the read succeeded */
+		iio_push_to_buffers_with_timestamp(indio_dev, &data,
+						   iio_get_time_ns(indio_dev));
+	}
+
+	iio_trigger_notify_done(indio_dev->trig);
+
+	return IRQ_HANDLED;
+}
+
 static int lmp92064_reset(struct lmp92064_adc_priv *priv,
 			  struct gpio_desc *gpio_reset)
 {
@@ -301,6 +345,12 @@ static int lmp92064_adc_probe(struct spi_device *spi)
 	indio_dev->channels = lmp92064_adc_channels;
 	indio_dev->num_channels = ARRAY_SIZE(lmp92064_adc_channels);
 	indio_dev->info = &lmp92064_adc_info;
+	indio_dev->available_scan_masks = lmp92064_scan_masks;
+
+	ret = devm_iio_triggered_buffer_setup(dev, indio_dev, NULL,
+					      lmp92064_trigger_handler, NULL);
+	if (ret)
+		return dev_err_probe(dev, ret, "Failed to setup buffered read\n");
 
 	return devm_iio_device_register(dev, indio_dev);
 }

base-commit: 9561de3a55bed6bdd44a12820ba81ec416e705a7
-- 
2.39.2