[PATCH 13/13] iio: adc: ad7380: add SPI offload support

[David Lechner <dlechner@xxxxxxxxxxxx>]

This extends the ad7380 ADC driver to use the offload capabilities of
capable SPI controllers. When offload support is available, a hardware
triggered buffer is used to allow sampling a high rates without CPU
intervention.

To keep things simple, when this feature is present in hardware we
disable the usual IIO triggered buffer and software timestamp rather
than trying to support multiple buffers.

Signed-off-by: David Lechner <dlechner@xxxxxxxxxxxx>
---
 drivers/iio/adc/Kconfig  |  1 +
 drivers/iio/adc/ad7380.c | 84 +++++++++++++++++++++++++++++++++++++++++++++---
 2 files changed, 80 insertions(+), 5 deletions(-)

diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
index cbfd626712e3..da44b585ea46 100644
--- a/drivers/iio/adc/Kconfig
+++ b/drivers/iio/adc/Kconfig
@@ -128,6 +128,7 @@ config AD7380
 	select IIO_BUFFER
 	select IIO_TRIGGER
 	select IIO_TRIGGERED_BUFFER
+	select IIO_HW_TRIGGERED_BUFFER
 	help
 	  AD7380 is a family of simultaneous sampling ADCs that share the same
 	  SPI register map and have similar pinouts.
diff --git a/drivers/iio/adc/ad7380.c b/drivers/iio/adc/ad7380.c
index 80712aaa9548..a71e8b81950b 100644
--- a/drivers/iio/adc/ad7380.c
+++ b/drivers/iio/adc/ad7380.c
@@ -20,6 +20,7 @@
 #include <linux/sysfs.h>
 
 #include <linux/iio/buffer.h>
+#include <linux/iio/hw_triggered_buffer.h>
 #include <linux/iio/iio.h>
 #include <linux/iio/sysfs.h>
 #include <linux/iio/trigger_consumer.h>
@@ -133,6 +134,7 @@ struct ad7380_state {
 	struct spi_device *spi;
 	struct regulator *vref;
 	struct regmap *regmap;
+	struct spi_offload *spi_offload;
 	/*
 	 * DMA (thus cache coherency maintenance) requires the
 	 * transfer buffers to live in their own cache lines.
@@ -335,6 +337,50 @@ static const struct iio_info ad7380_info = {
 	.debugfs_reg_access = &ad7380_debugfs_reg_access,
 };
 
+static int ad7380_buffer_preenable(struct iio_dev *indio_dev)
+{
+	struct ad7380_state *st = iio_priv(indio_dev);
+	struct spi_transfer xfer = {
+		.bits_per_word = st->chip_info->channels[0].scan_type.realbits,
+		.len = 4,
+		.rx_buf = SPI_OFFLOAD_RX_SENTINEL,
+	};
+
+	return spi_offload_prepare(st->spi_offload, st->spi, &xfer, 1);
+}
+
+static int ad7380_buffer_postenable(struct iio_dev *indio_dev)
+{
+	struct ad7380_state *st = iio_priv(indio_dev);
+
+	return spi_offload_enable(st->spi_offload);
+}
+
+static int ad7380_buffer_predisable(struct iio_dev *indio_dev)
+{
+	struct ad7380_state *st = iio_priv(indio_dev);
+
+	spi_offload_disable(st->spi_offload);
+
+	return 0;
+}
+
+static int ad7380_buffer_postdisable(struct iio_dev *indio_dev)
+{
+	struct ad7380_state *st = iio_priv(indio_dev);
+
+	spi_offload_unprepare(st->spi_offload);
+
+	return 0;
+}
+
+static const struct iio_buffer_setup_ops ad7380_buffer_ops = {
+	.preenable = &ad7380_buffer_preenable,
+	.postenable = &ad7380_buffer_postenable,
+	.predisable = &ad7380_buffer_predisable,
+	.postdisable = &ad7380_buffer_postdisable,
+};
+
 static int ad7380_init(struct ad7380_state *st)
 {
 	int ret;
@@ -417,11 +463,39 @@ static int ad7380_probe(struct spi_device *spi)
 	indio_dev->modes = INDIO_DIRECT_MODE;
 	indio_dev->available_scan_masks = ad7380_2_channel_scan_masks;
 
-	ret = devm_iio_triggered_buffer_setup(&spi->dev, indio_dev,
-					      iio_pollfunc_store_time,
-					      ad7380_trigger_handler, NULL);
-	if (ret)
-		return ret;
+	st->spi_offload = spi_offload_get(spi, 0);
+	if (IS_ERR(st->spi_offload)) {
+		ret = PTR_ERR(st->spi_offload);
+
+		if (ret == -EOPNOTSUPP)
+			st->spi_offload = NULL;
+		else
+			return dev_err_probe(&spi->dev, ret,
+					     "failed to get SPI offload\n");
+	}
+
+	if (st->spi_offload) {
+		/*
+		 * We can't have a soft timestamp (always last channel) when
+		 * using a hardware triggered buffer.
+		 */
+		indio_dev->num_channels -= 1;
+
+		ret = devm_iio_hw_triggered_buffer_setup(&spi->dev,
+							 indio_dev,
+							 st->spi_offload->dev,
+							 &ad7380_buffer_ops);
+		if (ret)
+			return dev_err_probe(&spi->dev, ret,
+					     "failed to setup offload\n");
+	} else {
+		ret = devm_iio_triggered_buffer_setup(&spi->dev, indio_dev,
+						      iio_pollfunc_store_time,
+						      ad7380_trigger_handler,
+						      NULL);
+		if (ret)
+			return ret;
+	}
 
 	ret = ad7380_init(st);
 	if (ret)

-- 
2.43.0