iio: adc: ad_sigma_delta: add SPI offload support

Add SPI offload support to the ad_sigma_delta module.

When the SPI controller has SPI offload capabilities, the module will
now use that for buffered reads instead of the RDY interrupt trigger.

Drivers that use the ad_sigma_delta module will have to opt into this
by setting supports_spi_offload since each driver will likely need
additional changes before SPI offload can be used. This will allow us
to gradually enable SPI offload support for each driver.

Signed-off-by: David Lechner <dlechner@baylibre.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Link: https://patch.msgid.link/20250701-iio-adc-ad7173-add-spi-offload-support-v3-11-42abb83e3dac@baylibre.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/ad_sigma_delta.c

@@ -20,6 +20,7 @@
 #include <linux/module.h>
 #include <linux/property.h>
 #include <linux/slab.h>
+#include <linux/spi/offload/consumer.h>
 #include <linux/spi/spi.h>
 #include <linux/spinlock.h>
 #include <linux/string.h>
@@ -27,6 +28,7 @@
 #include <linux/unaligned.h>
 
 #include <linux/iio/adc/ad_sigma_delta.h>
+#include <linux/iio/buffer-dmaengine.h>
 #include <linux/iio/buffer.h>
 #include <linux/iio/iio.h>
 #include <linux/iio/trigger_consumer.h>
@@ -467,8 +469,7 @@ 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 i, slot, channel;
-	unsigned int channel, scan_size;
 	u8 *samples_buf;
 	int ret;
 
@@ -496,25 +497,35 @@ static int ad_sd_buffer_postenable(struct iio_dev *indio_dev)
 	sigma_delta->active_slots = slot;
 	sigma_delta->current_slot = 0;
 
-	if (sigma_delta->active_slots > 1) {
+	if (ad_sigma_delta_has_spi_offload(sigma_delta)) {
-		ret = ad_sigma_delta_append_status(sigma_delta, true);
+		xfer[1].offload_flags = SPI_OFFLOAD_XFER_RX_STREAM;
-		if (ret)
+		xfer[1].bits_per_word = scan_type->realbits;
-			return ret;
+		xfer[1].len = spi_bpw_to_bytes(scan_type->realbits);
+	} else {
+		unsigned int samples_buf_size, scan_size;
+
+		if (sigma_delta->active_slots > 1) {
+			ret = ad_sigma_delta_append_status(sigma_delta, true);
+			if (ret)
+				return ret;
+		}
+
+		samples_buf_size =
+			ALIGN(slot * BITS_TO_BYTES(scan_type->storagebits),
+			      sizeof(s64));
+		samples_buf_size += sizeof(s64);
+		samples_buf = devm_krealloc(&sigma_delta->spi->dev,
+					    sigma_delta->samples_buf,
+					    samples_buf_size, GFP_KERNEL);
+		if (!samples_buf)
+			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);
 	}
-
-	samples_buf_size = ALIGN(slot * BITS_TO_BYTES(scan_type->storagebits),
-				 sizeof(s64));
-	samples_buf_size += sizeof(s64);
-	samples_buf = devm_krealloc(&sigma_delta->spi->dev, sigma_delta->samples_buf,
-				    samples_buf_size, GFP_KERNEL);
-	if (!samples_buf)
-		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) {
@@ -530,6 +541,8 @@ static int ad_sd_buffer_postenable(struct iio_dev *indio_dev)
 						&xfer[1], 1);
 	}
 
+	sigma_delta->sample_msg.offload = sigma_delta->offload;
+
 	ret = spi_optimize_message(sigma_delta->spi, &sigma_delta->sample_msg);
 	if (ret)
 		return ret;
@@ -546,7 +559,19 @@ static int ad_sd_buffer_postenable(struct iio_dev *indio_dev)
 	if (ret)
 		goto err_unlock;
 
-	ad_sd_enable_irq(sigma_delta);
+	if (ad_sigma_delta_has_spi_offload(sigma_delta)) {
+		struct spi_offload_trigger_config config = {
+			.type = SPI_OFFLOAD_TRIGGER_DATA_READY,
+		};
+
+		ret = spi_offload_trigger_enable(sigma_delta->offload,
+						 sigma_delta->offload_trigger,
+						 &config);
+		if (ret)
+			goto err_unlock;
+	} else {
+		ad_sd_enable_irq(sigma_delta);
+	}
 
 	return 0;
 
@@ -561,10 +586,15 @@ static int ad_sd_buffer_postdisable(struct iio_dev *indio_dev)
 {
 	struct ad_sigma_delta *sigma_delta = iio_device_get_drvdata(indio_dev);
 
-	reinit_completion(&sigma_delta->completion);
+	if (ad_sigma_delta_has_spi_offload(sigma_delta)) {
-	wait_for_completion_timeout(&sigma_delta->completion, HZ);
+		spi_offload_trigger_disable(sigma_delta->offload,
+					    sigma_delta->offload_trigger);
+	} else {
+		reinit_completion(&sigma_delta->completion);
+		wait_for_completion_timeout(&sigma_delta->completion, HZ);
 
-	ad_sd_disable_irq(sigma_delta);
+		ad_sd_disable_irq(sigma_delta);
+	}
 
 	sigma_delta->keep_cs_asserted = false;
 	ad_sigma_delta_set_mode(sigma_delta, AD_SD_MODE_IDLE);
@@ -679,7 +709,8 @@ static irqreturn_t ad_sd_data_rdy_trig_poll(int irq, void *private)
 	if ((!sigma_delta->rdy_gpiod || gpiod_get_value(sigma_delta->rdy_gpiod)) &&
 	    ad_sd_disable_irq(sigma_delta)) {
 		complete(&sigma_delta->completion);
-		iio_trigger_poll(sigma_delta->trig);
+		if (sigma_delta->trig)
+			iio_trigger_poll(sigma_delta->trig);
 
 		return IRQ_HANDLED;
 	}
@@ -712,17 +743,6 @@ static int devm_ad_sd_probe_trigger(struct device *dev, struct iio_dev *indio_de
 	unsigned long irq_flags = irq_get_trigger_type(sigma_delta->irq_line);
 	int ret;
 
-	if (dev != &sigma_delta->spi->dev) {
-		dev_err(dev, "Trigger parent should be '%s', got '%s'\n",
-			dev_name(dev), dev_name(&sigma_delta->spi->dev));
-		return -EFAULT;
-	}
-
-	sigma_delta->trig = devm_iio_trigger_alloc(dev, "%s-dev%d", indio_dev->name,
-						   iio_device_id(indio_dev));
-	if (sigma_delta->trig == NULL)
-		return -ENOMEM;
-
 	init_completion(&sigma_delta->completion);
 
 	sigma_delta->irq_dis = true;
@@ -742,14 +762,33 @@ static int devm_ad_sd_probe_trigger(struct device *dev, struct iio_dev *indio_de
 	if (ret)
 		return ret;
 
-	iio_trigger_set_drvdata(sigma_delta->trig, sigma_delta);
+	if (ad_sigma_delta_has_spi_offload(sigma_delta)) {
+		sigma_delta->offload_trigger =
+			devm_spi_offload_trigger_get(dev, sigma_delta->offload,
+						     SPI_OFFLOAD_TRIGGER_DATA_READY);
+		if (IS_ERR(sigma_delta->offload_trigger))
+			return dev_err_probe(dev, PTR_ERR(sigma_delta->offload_trigger),
+					     "Failed to get SPI offload trigger\n");
+	} else {
+		if (dev != &sigma_delta->spi->dev)
+			return dev_err_probe(dev, -EFAULT,
+				"Trigger parent should be '%s', got '%s'\n",
+				dev_name(dev), dev_name(&sigma_delta->spi->dev));
 
-	ret = devm_iio_trigger_register(dev, sigma_delta->trig);
+		sigma_delta->trig = devm_iio_trigger_alloc(dev, "%s-dev%d",
-	if (ret)
+			indio_dev->name, iio_device_id(indio_dev));
-		return ret;
+		if (!sigma_delta->trig)
+			return -ENOMEM;
 
-	/* select default trigger */
+		iio_trigger_set_drvdata(sigma_delta->trig, sigma_delta);
-	indio_dev->trig = iio_trigger_get(sigma_delta->trig);
+
+		ret = devm_iio_trigger_register(dev, sigma_delta->trig);
+		if (ret)
+			return ret;
+
+		/* select default trigger */
+		indio_dev->trig = iio_trigger_get(sigma_delta->trig);
+	}
 
 	return 0;
 }
@@ -769,12 +808,29 @@ int devm_ad_sd_setup_buffer_and_trigger(struct device *dev, struct iio_dev *indi
 	if (!sigma_delta->slots)
 		return -ENOMEM;
 
-	ret = devm_iio_triggered_buffer_setup(dev, indio_dev,
+	if (ad_sigma_delta_has_spi_offload(sigma_delta)) {
-					      &iio_pollfunc_store_time,
+		struct dma_chan *rx_dma;
-					      &ad_sd_trigger_handler,
+
-					      &ad_sd_buffer_setup_ops);
+		rx_dma = devm_spi_offload_rx_stream_request_dma_chan(dev,
-	if (ret)
+			sigma_delta->offload);
-		return ret;
+		if (IS_ERR(rx_dma))
+			return dev_err_probe(dev, PTR_ERR(rx_dma),
+					     "Failed to get RX DMA channel\n");
+
+		ret = devm_iio_dmaengine_buffer_setup_with_handle(dev, indio_dev,
+			rx_dma, IIO_BUFFER_DIRECTION_IN);
+		if (ret)
+			return dev_err_probe(dev, ret, "Cannot setup DMA buffer\n");
+
+		indio_dev->setup_ops = &ad_sd_buffer_setup_ops;
+	} else {
+		ret = devm_iio_triggered_buffer_setup(dev, indio_dev,
+						      &iio_pollfunc_store_time,
+						      &ad_sd_trigger_handler,
+						      &ad_sd_buffer_setup_ops);
+		if (ret)
+			return ret;
+	}
 
 	return devm_ad_sd_probe_trigger(dev, indio_dev);
 }
@@ -837,6 +893,20 @@ int ad_sd_init(struct ad_sigma_delta *sigma_delta, struct iio_dev *indio_dev,
 			return sigma_delta->irq_line;
 	}
 
+	if (info->supports_spi_offload) {
+		struct spi_offload_config offload_config = {
+			.capability_flags = SPI_OFFLOAD_CAP_TRIGGER |
+					    SPI_OFFLOAD_CAP_RX_STREAM_DMA,
+		};
+		int ret;
+
+		sigma_delta->offload = devm_spi_offload_get(&spi->dev, spi,
+							    &offload_config);
+		ret = PTR_ERR_OR_ZERO(sigma_delta->offload);
+		if (ret && ret != -ENODEV)
+			return dev_err_probe(&spi->dev, ret, "Failed to get SPI offload\n");
+	}
+
 	iio_device_set_drvdata(indio_dev, sigma_delta);
 
 	return 0;
@@ -846,3 +916,4 @@ EXPORT_SYMBOL_NS_GPL(ad_sd_init, "IIO_AD_SIGMA_DELTA");
 MODULE_AUTHOR("Lars-Peter Clausen <lars@metafoo.de>");
 MODULE_DESCRIPTION("Analog Devices Sigma-Delta ADCs");
 MODULE_LICENSE("GPL v2");
+MODULE_IMPORT_NS("IIO_DMAENGINE_BUFFER");

include/linux/iio/adc/ad_sigma_delta.h

@@ -31,6 +31,8 @@ struct ad_sigma_delta;
 struct device;
 struct gpio_desc;
 struct iio_dev;
+struct spi_offload;
+struct spi_offload_trigger;
 
 /**
  * struct ad_sigma_delta_info - Sigma Delta driver specific callbacks and options
@@ -47,6 +49,10 @@ struct iio_dev;
  * @has_registers: true if the device has writable and readable registers, false
  *		if there is just one read-only sample data shift register.
  * @has_named_irqs: Set to true if there is more than one IRQ line.
+ * @supports_spi_offload: Set to true if the driver supports SPI offload. Often
+ *		special considerations are needed for scan_type and other channel
+ *		info, so individual drivers have to set this to let the core
+ *		code know that it can use SPI offload if it is available.
  * @addr_shift: Shift of the register address in the communications register.
  * @read_mask: Mask for the communications register having the read bit set.
  * @status_ch_mask: Mask for the channel number stored in status register.
@@ -65,6 +71,7 @@ struct ad_sigma_delta_info {
 	int (*postprocess_sample)(struct ad_sigma_delta *, unsigned int raw_sample);
 	bool has_registers;
 	bool has_named_irqs;
+	bool supports_spi_offload;
 	unsigned int addr_shift;
 	unsigned int read_mask;
 	unsigned int status_ch_mask;
@@ -108,6 +115,8 @@ struct ad_sigma_delta {
 	struct spi_message	sample_msg;
 	struct spi_transfer	sample_xfer[2];
 	u8			*samples_buf;
+	struct spi_offload	*offload;
+	struct spi_offload_trigger *offload_trigger;
 
 	/*
 	 * DMA (thus cache coherency maintenance) requires the
@@ -121,6 +130,11 @@ struct ad_sigma_delta {
 	u8				sample_addr;
 };
 
+static inline bool ad_sigma_delta_has_spi_offload(struct ad_sigma_delta *sd)
+{
+	return sd->offload != NULL;
+}
+
 static inline int ad_sigma_delta_set_channel(struct ad_sigma_delta *sd,
 	unsigned int channel)
 {