[PATCH v3 08/12] iio: adc: ad_sigma_delta: use spi_optimize_message()

[David Lechner <dlechner@baylibre.com>]

Use spi_optimize_message() to improve the performance of buffered reads.

By setting up the SPI message and pre-optimizing it in the buffer
postenable callback, we can reduce overhead during each sample read.

A rough estimate shows that this reduced the CPU usage of the interrupt
handler thread from 22% to 16% using an EVAL-AD4112ARDZ board on a
DE10-Nano (measuring a single channel at the default 6.2 kHz sample
rate).

Signed-off-by: David Lechner <dlechner@baylibre.com>
---
 drivers/iio/adc/ad_sigma_delta.c       | 72 ++++++++++++++++------------------
 include/linux/iio/adc/ad_sigma_delta.h |  3 ++
 2 files changed, 37 insertions(+), 38 deletions(-)

diff --git a/drivers/iio/adc/ad_sigma_delta.c b/drivers/iio/adc/ad_sigma_delta.c
index ce549775ac3d68fd11e660b6b993ac661301756a..124c42e19f2e25723b67ea38f7d016f00ff91342 100644
--- a/drivers/iio/adc/ad_sigma_delta.c
+++ b/drivers/iio/adc/ad_sigma_delta.c
@@ -466,8 +466,9 @@ static int ad_sd_buffer_postenable(struct iio_dev *indio_dev)
 {
 	struct ad_sigma_delta *sigma_delta = iio_device_get_drvdata(indio_dev);
 	const struct iio_scan_type *scan_type = &indio_dev->channels[0].scan_type;
+	struct spi_transfer *xfer = sigma_delta->sample_xfer;
 	unsigned int i, slot, samples_buf_size;
-	unsigned int channel;
+	unsigned int channel, scan_size;
 	u8 *samples_buf;
 	int ret;
 
@@ -510,6 +511,28 @@ static int ad_sd_buffer_postenable(struct iio_dev *indio_dev)
 		return -ENOMEM;
 
 	sigma_delta->samples_buf = samples_buf;
+	scan_size = BITS_TO_BYTES(scan_type->realbits + scan_type->shift);
+	/* For 24-bit data, there is an extra byte of padding. */
+	xfer[1].rx_buf = &sigma_delta->rx_buf[scan_size == 3 ? 1 : 0];
+	xfer[1].len = scan_size + (sigma_delta->status_appended ? 1 : 0);
+	xfer[1].cs_change = 1;
+
+	if (sigma_delta->info->has_registers) {
+		xfer[0].tx_buf = &sigma_delta->sample_addr;
+		xfer[0].len = 1;
+
+		ad_sd_set_read_reg_addr(sigma_delta,
+					sigma_delta->info->data_reg ?: AD_SD_REG_DATA,
+					&sigma_delta->sample_addr);
+		spi_message_init_with_transfers(&sigma_delta->sample_msg, xfer, 2);
+	} else {
+		spi_message_init_with_transfers(&sigma_delta->sample_msg,
+						&xfer[1], 1);
+	}
+
+	ret = spi_optimize_message(sigma_delta->spi, &sigma_delta->sample_msg);
+	if (ret)
+		return ret;
 
 	spi_bus_lock(sigma_delta->spi->controller);
 	sigma_delta->bus_locked = true;
@@ -529,6 +552,7 @@ static int ad_sd_buffer_postenable(struct iio_dev *indio_dev)
 
 err_unlock:
 	spi_bus_unlock(sigma_delta->spi->controller);
+	spi_unoptimize_message(&sigma_delta->sample_msg);
 
 	return ret;
 }
@@ -550,7 +574,10 @@ static int ad_sd_buffer_postdisable(struct iio_dev *indio_dev)
 
 	ad_sigma_delta_disable_all(sigma_delta);
 	sigma_delta->bus_locked = false;
-	return spi_bus_unlock(sigma_delta->spi->controller);
+	spi_bus_unlock(sigma_delta->spi->controller);
+	spi_unoptimize_message(&sigma_delta->sample_msg);
+
+	return 0;
 }
 
 static irqreturn_t ad_sd_trigger_handler(int irq, void *p)
@@ -560,50 +587,19 @@ static irqreturn_t ad_sd_trigger_handler(int irq, void *p)
 	const struct iio_scan_type *scan_type = &indio_dev->channels[0].scan_type;
 	struct ad_sigma_delta *sigma_delta = iio_device_get_drvdata(indio_dev);
 	u8 *data = sigma_delta->rx_buf;
-	unsigned int transfer_size;
 	unsigned int sample_size;
 	unsigned int sample_pos;
 	unsigned int status_pos;
 	unsigned int reg_size;
-	unsigned int data_reg;
+	int ret;
 
 	reg_size = BITS_TO_BYTES(scan_type->realbits + scan_type->shift);
+	/* For 24-bit data, there is an extra byte of padding. */
+	status_pos = reg_size + (reg_size == 3 ? 1 : 0);
 
-	if (sigma_delta->info->data_reg != 0)
-		data_reg = sigma_delta->info->data_reg;
-	else
-		data_reg = AD_SD_REG_DATA;
-
-	/* Status word will be appended to the sample during transfer */
-	if (sigma_delta->status_appended)
-		transfer_size = reg_size + 1;
-	else
-		transfer_size = reg_size;
-
-	switch (reg_size) {
-	case 4:
-	case 2:
-	case 1:
-		status_pos = reg_size;
-		ad_sd_read_reg_raw(sigma_delta, data_reg, transfer_size, &data[0]);
-		break;
-	case 3:
-		/*
-		 * Data array after transfer will look like (if status is appended):
-		 * data[] = { [0][sample][sample][sample][status] }
-		 * Keeping the first byte 0 shifts the status position by 1 byte to the right.
-		 */
-		status_pos = reg_size + 1;
-
-		/* We store 24 bit samples in a 32 bit word. Keep the upper
-		 * byte set to zero. */
-		ad_sd_read_reg_raw(sigma_delta, data_reg, transfer_size, &data[1]);
-		break;
-
-	default:
-		dev_err_ratelimited(&indio_dev->dev, "Unsupported reg_size: %u\n", reg_size);
+	ret = spi_sync_locked(sigma_delta->spi, &sigma_delta->sample_msg);
+	if (ret)
 		goto irq_handled;
-	}
 
 	/*
 	 * For devices sampling only one channel at
diff --git a/include/linux/iio/adc/ad_sigma_delta.h b/include/linux/iio/adc/ad_sigma_delta.h
index 5056677c9941afadc2383febbcafeb02e23a4f44..2037bb68b44115681ff48f66b580b63f50c2ea9e 100644
--- a/include/linux/iio/adc/ad_sigma_delta.h
+++ b/include/linux/iio/adc/ad_sigma_delta.h
@@ -105,6 +105,8 @@ struct ad_sigma_delta {
 	bool			status_appended;
 	/* map slots to channels in order to know what to expect from devices */
 	unsigned int		*slots;
+	struct spi_message	sample_msg;
+	struct spi_transfer	sample_xfer[2];
 	u8			*samples_buf;
 
 	/*
@@ -116,6 +118,7 @@ struct ad_sigma_delta {
 	 */
 	u8				tx_buf[4] __aligned(IIO_DMA_MINALIGN);
 	u8				rx_buf[16] __aligned(8);
+	u8				sample_addr;
 };
 
 static inline int ad_sigma_delta_set_channel(struct ad_sigma_delta *sd,

-- 
2.43.0