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>
---
 drivers/iio/adc/ad_sigma_delta.c       | 160 +++++++++++++++++++++++----------
 include/linux/iio/adc/ad_sigma_delta.h |  14 +++
 2 files changed, 129 insertions(+), 45 deletions(-)

diff --git a/drivers/iio/adc/ad_sigma_delta.c b/drivers/iio/adc/ad_sigma_delta.c
index a9b97f5d4107a2e1bb74877d30403445e9b04a44..449b0756be96d3f864a6e7f070467ad7311bf7d5 100644
--- a/drivers/iio/adc/ad_sigma_delta.c
+++ b/drivers/iio/adc/ad_sigma_delta.c
@@ -14,11 +14,13 @@
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/slab.h>
+#include <linux/spi/offload/consumer.h>
 #include <linux/spi/spi.h>
 #include <linux/types.h>
 #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/sysfs.h>
@@ -460,8 +462,7 @@ 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 channel, scan_size;
+	unsigned int i, slot, channel;
 	u8 *samples_buf;
 	int ret;
 
@@ -489,23 +490,33 @@ 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) {
-		ret = ad_sigma_delta_append_status(sigma_delta, true);
-		if (ret)
-			return ret;
-	}
+	if (ad_sigma_delta_has_spi_offload(sigma_delta)) {
+		xfer[1].offload_flags = SPI_OFFLOAD_XFER_RX_STREAM;
+		xfer[1].bits_per_word = scan_type->realbits;
+		xfer[1].len = spi_bpw_to_bytes(scan_type->realbits);
+	} else {
+		unsigned int samples_buf_size, scan_size;
 
-	samples_buf_size = ALIGN(slot * scan_type->storagebits, 8);
-	samples_buf_size += sizeof(int64_t);
-	samples_buf = devm_krealloc(&sigma_delta->spi->dev, sigma_delta->samples_buf,
-				    samples_buf_size, GFP_KERNEL);
-	if (!samples_buf)
-		return -ENOMEM;
+		if (sigma_delta->active_slots > 1) {
+			ret = ad_sigma_delta_append_status(sigma_delta, true);
+			if (ret)
+				return ret;
+		}
 
-	sigma_delta->samples_buf = samples_buf;
-	scan_size = BITS_TO_BYTES(scan_type->realbits + scan_type->shift);
-	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 * scan_type->storagebits, 8);
+		samples_buf_size += sizeof(int64_t);
+		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);
+
+		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) {
@@ -521,6 +532,8 @@ 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;
@@ -537,7 +550,19 @@ 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;
 
@@ -552,10 +577,15 @@ 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);
-	wait_for_completion_timeout(&sigma_delta->completion, HZ);
+	if (ad_sigma_delta_has_spi_offload(sigma_delta)) {
+		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);
@@ -670,7 +700,8 @@ 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;
 	}
@@ -703,17 +734,6 @@ 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;
@@ -733,14 +753,33 @@ 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);
-	if (ret)
-		return ret;
+		sigma_delta->trig = devm_iio_trigger_alloc(dev, "%s-dev%d",
+			indio_dev->name, iio_device_id(indio_dev));
+		if (!sigma_delta->trig)
+			return -ENOMEM;
 
-	/* select default trigger */
-	indio_dev->trig = iio_trigger_get(sigma_delta->trig);
+		iio_trigger_set_drvdata(sigma_delta->trig, sigma_delta);
+
+		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;
 }
@@ -760,12 +799,29 @@ 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,
-					      &iio_pollfunc_store_time,
-					      &ad_sd_trigger_handler,
-					      &ad_sd_buffer_setup_ops);
-	if (ret)
-		return ret;
+	if (ad_sigma_delta_has_spi_offload(sigma_delta)) {
+		struct dma_chan *rx_dma;
+
+		rx_dma = devm_spi_offload_rx_stream_request_dma_chan(dev,
+			sigma_delta->offload);
+		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);
 }
@@ -828,6 +884,20 @@ 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;
diff --git a/include/linux/iio/adc/ad_sigma_delta.h b/include/linux/iio/adc/ad_sigma_delta.h
index 2037bb68b44115681ff48f66b580b63f50c2ea9e..6e70a412e218d54bbf9bb6861b1a4cc89be868e8 100644
--- a/include/linux/iio/adc/ad_sigma_delta.h
+++ b/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)
 {

-- 
2.43.0

Hi David,

kernel test robot noticed the following build errors:

[auto build test ERROR on d02f330b0c78bcf76643fbb7d3215a58b181f829]

url:    https://github.com/intel-lab-lkp/linux/commits/David-Lechner/iio-adc-ad_sigma_delta-sort-includes/20250621-063127
base:   d02f330b0c78bcf76643fbb7d3215a58b181f829
patch link:    https://lore.kernel.org/r/20250620-iio-adc-ad7173-add-spi-offload-support-v1-8-0766f6297430%40baylibre.com
patch subject: [PATCH 8/9] iio: adc: ad_sigma_delta: add SPI offload support
config: x86_64-buildonly-randconfig-001-20250621 (https://download.01.org/0day-ci/archive/20250623/202506232119.aLbzgQow-lkp@intel.com/config)
compiler: gcc-12 (Debian 12.2.0-14) 12.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250623/202506232119.aLbzgQow-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202506232119.aLbzgQow-lkp@intel.com/

All errors (new ones prefixed by >>, old ones prefixed by <<):

>> ERROR: modpost: module ad_sigma_delta uses symbol devm_iio_dmaengine_buffer_setup_with_handle from namespace IIO_DMAENGINE_BUFFER, but does not import it.

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Hi David,

kernel test robot noticed the following build warnings:

[auto build test WARNING on d02f330b0c78bcf76643fbb7d3215a58b181f829]

url:    https://github.com/intel-lab-lkp/linux/commits/David-Lechner/iio-adc-ad_sigma_delta-sort-includes/20250621-063127
base:   d02f330b0c78bcf76643fbb7d3215a58b181f829
patch link:    https://lore.kernel.org/r/20250620-iio-adc-ad7173-add-spi-offload-support-v1-8-0766f6297430%40baylibre.com
patch subject: [PATCH 8/9] iio: adc: ad_sigma_delta: add SPI offload support
config: x86_64-buildonly-randconfig-004-20250621 (https://download.01.org/0day-ci/archive/20250623/202506231738.CgeNexV4-lkp@intel.com/config)
compiler: gcc-12 (Debian 12.2.0-14) 12.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250623/202506231738.CgeNexV4-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202506231738.CgeNexV4-lkp@intel.com/

All warnings (new ones prefixed by >>, old ones prefixed by <<):

>> WARNING: modpost: module ad_sigma_delta uses symbol devm_iio_dmaengine_buffer_setup_with_handle from namespace IIO_DMAENGINE_BUFFER, but does not import it.

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

On Fri, 20 Jun 2025 17:20:14 -0500
David Lechner <dlechner@baylibre.com> wrote:

> 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>

A few queries inline that again are more about the original code than what
you change here.

Jonathan

> ---
>  drivers/iio/adc/ad_sigma_delta.c       | 160 +++++++++++++++++++++++----------
>  include/linux/iio/adc/ad_sigma_delta.h |  14 +++
>  2 files changed, 129 insertions(+), 45 deletions(-)
> 
> diff --git a/drivers/iio/adc/ad_sigma_delta.c b/drivers/iio/adc/ad_sigma_delta.c
> index a9b97f5d4107a2e1bb74877d30403445e9b04a44..449b0756be96d3f864a6e7f070467ad7311bf7d5 100644
> --- a/drivers/iio/adc/ad_sigma_delta.c
> +++ b/drivers/iio/adc/ad_sigma_delta.c
> @@ -14,11 +14,13 @@
>  #include <linux/kernel.h>
>  #include <linux/module.h>
>  #include <linux/slab.h>
> +#include <linux/spi/offload/consumer.h>
>  #include <linux/spi/spi.h>
>  #include <linux/types.h>
>  #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/sysfs.h>
> @@ -460,8 +462,7 @@ 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 channel, scan_size;
> +	unsigned int i, slot, channel;
>  	u8 *samples_buf;
>  	int ret;
>  
> @@ -489,23 +490,33 @@ 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) {
> -		ret = ad_sigma_delta_append_status(sigma_delta, true);
> -		if (ret)
> -			return ret;
> -	}
> +	if (ad_sigma_delta_has_spi_offload(sigma_delta)) {
> +		xfer[1].offload_flags = SPI_OFFLOAD_XFER_RX_STREAM;
> +		xfer[1].bits_per_word = scan_type->realbits;
> +		xfer[1].len = spi_bpw_to_bytes(scan_type->realbits);
> +	} else {
> +		unsigned int samples_buf_size, scan_size;
>  
> -	samples_buf_size = ALIGN(slot * scan_type->storagebits, 8);
> -	samples_buf_size += sizeof(int64_t);
> -	samples_buf = devm_krealloc(&sigma_delta->spi->dev, sigma_delta->samples_buf,
> -				    samples_buf_size, GFP_KERNEL);
> -	if (!samples_buf)
> -		return -ENOMEM;
> +		if (sigma_delta->active_slots > 1) {
> +			ret = ad_sigma_delta_append_status(sigma_delta, true);
> +			if (ret)
> +				return ret;
> +		}
>  
> -	sigma_delta->samples_buf = samples_buf;
> -	scan_size = BITS_TO_BYTES(scan_type->realbits + scan_type->shift);
> -	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 * scan_type->storagebits, 8);

The code I queried earlier is moved here, so make sure to carry through
any changes if it is indeed wrong!

> +		samples_buf_size += sizeof(int64_t);
> +		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);
> +
> +		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) {

> @@ -670,7 +700,8 @@ 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)

Is this defensive or can we actually get here with out a trigger?
I would have thought in the offload case (so no trigger here) we'd not call this
function at all.  Mind you, can't we get here with no trigger when doing
a calibration or simple read normally?  

> +			iio_trigger_poll(sigma_delta->trig);
>  
>  		return IRQ_HANDLED;
>  	}

On 6/22/25 10:00 AM, Jonathan Cameron wrote:
> On Fri, 20 Jun 2025 17:20:14 -0500
> David Lechner <dlechner@baylibre.com> wrote:
> 
>> Add SPI offload support to the ad_sigma_delta module.
>>

...

>> @@ -670,7 +700,8 @@ 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)
> 
> Is this defensive or can we actually get here with out a trigger?
> I would have thought in the offload case (so no trigger here) we'd not call this
> function at all.  Mind you, can't we get here with no trigger when doing
> a calibration or simple read normally?  

The difference is that with SPI offload, sigma_delta->trig is NULL
but without SPI offload, it is never NULL. iio_trigger_poll() doesn't
check for NULL and would crash with NULL pointer dereference.

During calibration and single conversion the poll function isn't
attached to the trigger, so I guess that is why it didn't really
hurt to call iio_trigger_poll() in that case.

> 
>> +			iio_trigger_poll(sigma_delta->trig);
>>  
>>  		return IRQ_HANDLED;
>>  	}
> 
>