iio: adc: ad7768-1: use new spi-engine implementation

Add  support for new spi-engine implementation on ad7768-1 driver,
optimizing offload transfers by reducing CS delay and minimizing
the number of commands in the offload FIFO.

Without the otimization, there's not enough time between the end of a
transfer and the start of the next one, reducing the actual sample rate.

Adjust 'tx_data' buffer handling in SPI register read and write functions
to ensure endianness consistency with the new spi-engine.

Signed-off-by: Jonathan Santos <Jonathan.Santos@analog.com>

Author: jonathanns

drivers/iio/adc/ad7768-1.c

@@ -22,7 +22,7 @@
 #include <linux/sysfs.h>
 #include "linux/util_macros.h"
 #include <linux/spi/spi.h>
-#include <linux/spi/spi-engine.h>
+#include <linux/spi/spi-engine-ex.h>
 
 #include <linux/iio/buffer.h>
 #include <linux/iio/buffer-dma.h>
@@ -289,6 +289,8 @@ struct ad7768_state {
 	struct mutex lock;
 	struct clk *mclk;
 	struct gpio_chip gpiochip;
+	struct spi_transfer offload_xfer;
+	struct spi_message offload_msg;
 	unsigned int gpio_avail_map;
 	unsigned int mclk_freq;
 	unsigned int mclk_div;
@@ -329,11 +331,11 @@ static int ad7768_spi_reg_read(struct ad7768_state *st, unsigned int addr,
 		.len = len + 1,
 		.bits_per_word = (len == 3 ? 32 : 16),
 	};
-	unsigned char tx_data[4];
+	u32 tx_data;
 	int ret;
 
-	tx_data[0] = AD7768_RD_FLAG_MSK(addr);
-	xfer.tx_buf = tx_data;
+	tx_data = AD7768_RD_FLAG_MSK(addr) << (len * 8);
+	xfer.tx_buf = &tx_data;
 	ret = spi_sync_transfer(st->spi, &xfer, 1);
 	if (ret < 0)
 		return ret;
@@ -351,11 +353,11 @@ static int ad7768_spi_reg_write(struct ad7768_state *st,
 		.len = 2,
 		.bits_per_word = 16,
 	};
-	unsigned char tx_data[2];
+	u16 tx_data;
 
-	tx_data[0] = AD7768_WR_FLAG_MSK(addr);
-	tx_data[1] = val & 0xFF;
-	xfer.tx_buf = tx_data;
+	tx_data = AD7768_WR_FLAG_MSK(addr) << 8;
+	tx_data |= val & 0xFF;
+	xfer.tx_buf = &tx_data;
 	return spi_sync_transfer(st->spi, &xfer, 1);
 }
 
@@ -1107,18 +1109,14 @@ static int ad7768_buffer_postenable(struct iio_dev *indio_dev)
 {
 	struct ad7768_state *st = iio_priv(indio_dev);
 	const struct iio_scan_type *scan_type;
-	struct spi_transfer xfer = {
-		.len = 1,
-	};
-	unsigned int rx_data[2];
-	struct spi_message msg;
 	int ret;
 
 	scan_type = iio_get_current_scan_type(indio_dev, &indio_dev->channels[0]);
 	if (IS_ERR(scan_type))
 		return PTR_ERR(scan_type);
 
-	xfer.bits_per_word = scan_type->realbits;
+	st->offload_xfer.len = roundup_pow_of_two(BITS_TO_BYTES(scan_type->realbits));
+	st->offload_xfer.bits_per_word = scan_type->realbits;
 
 	/*
 	* Write a 1 to the LSB of the INTERFACE_FORMAT register to enter
@@ -1130,14 +1128,20 @@ static int ad7768_buffer_postenable(struct iio_dev *indio_dev)
 		return ret;
 
 	if (st->spi_is_dma_mapped) {
+		/* HACK: invalid pointer indicates read data from SPI offload DMA */
+		st->offload_xfer.rx_buf = (void *)(-1);
+		spi_message_init_with_transfers(&st->offload_msg, &st->offload_xfer, 1);
+
+		ret = spi_optimize_message(st->spi, &st->offload_msg);
+		if (ret < 0)
+			return ret;
+
 		spi_bus_lock(st->spi->master);
 
-		xfer.rx_buf = rx_data;
-		spi_message_init_with_transfers(&msg, &xfer, 1);
-		ret = spi_engine_offload_load_msg(st->spi, &msg);
+		ret = spi_engine_ex_offload_load_msg(st->spi, &st->offload_msg);
 		if (ret < 0)
 			return ret;
-		spi_engine_offload_enable(st->spi, true);
+		spi_engine_ex_offload_enable(st->spi, true);
 	}
 
 	return ret;
@@ -1149,9 +1153,10 @@ static int ad7768_buffer_predisable(struct iio_dev *indio_dev)
 	unsigned int regval;
 
 	if (st->spi_is_dma_mapped) {
-		spi_engine_offload_enable(st->spi, false);
+		spi_engine_ex_offload_enable(st->spi, false);
 		spi_bus_unlock(st->spi->master);
 	}
+	spi_unoptimize_message(&st->offload_msg);
 
 	/*
 	 * To exit continuous read mode, perform a single read of the ADC_DATA
@@ -1285,7 +1290,7 @@ static int ad7768_probe(struct spi_device *spi)
 		return PTR_ERR(st->mclk);
 
 	st->mclk_freq = clk_get_rate(st->mclk);
-	st->spi_is_dma_mapped = spi_engine_offload_supported(spi);
+	st->spi_is_dma_mapped = spi_engine_ex_offload_supported(spi);
 	st->irq = spi->irq;
 
 	mutex_init(&st->lock);