[PATCH] iio: adc: stm32-dfsdm: fix sleep in atomic context

[Olivier Moysan <olivier.moysan@st.com>]

This commit fixes the error message:
"BUG: sleeping function called from invalid context at kernel/irq/chip.c"
Suppress the trigger irq handler. Make the buffer transfers directly
in DMA callback, instead.
Push buffers without timestamps, as timestamps are not supported
in DFSDM driver.

Fixes: 11646e81d775 ("iio: adc: stm32-dfsdm: add support for buffer modes")

Signed-off-by: Olivier Moysan <olivier.moysan@st.com>
---
There is the same issue on STM32 ADC driver.
The solution for ADC driver has been already discussed in the thread
https://lkml.org/lkml/2019/3/30/171
The current patch for STM32 DFSDM driver, bypasses the IIO IRQ trigger
handler, as proposed in this thread.
---
 drivers/iio/adc/stm32-dfsdm-adc.c | 43 +++++++------------------------
 1 file changed, 10 insertions(+), 33 deletions(-)

diff --git a/drivers/iio/adc/stm32-dfsdm-adc.c b/drivers/iio/adc/stm32-dfsdm-adc.c
index 2aad2cda6943..76a60d93fe23 100644
--- a/drivers/iio/adc/stm32-dfsdm-adc.c
+++ b/drivers/iio/adc/stm32-dfsdm-adc.c
@@ -842,31 +842,6 @@ static inline void stm32_dfsdm_process_data(struct stm32_dfsdm_adc *adc,
 	}
 }
 
-static irqreturn_t stm32_dfsdm_adc_trigger_handler(int irq, void *p)
-{
-	struct iio_poll_func *pf = p;
-	struct iio_dev *indio_dev = pf->indio_dev;
-	struct stm32_dfsdm_adc *adc = iio_priv(indio_dev);
-	int available = stm32_dfsdm_adc_dma_residue(adc);
-
-	while (available >= indio_dev->scan_bytes) {
-		s32 *buffer = (s32 *)&adc->rx_buf[adc->bufi];
-
-		stm32_dfsdm_process_data(adc, buffer);
-
-		iio_push_to_buffers_with_timestamp(indio_dev, buffer,
-						   pf->timestamp);
-		available -= indio_dev->scan_bytes;
-		adc->bufi += indio_dev->scan_bytes;
-		if (adc->bufi >= adc->buf_sz)
-			adc->bufi = 0;
-	}
-
-	iio_trigger_notify_done(indio_dev->trig);
-
-	return IRQ_HANDLED;
-}
-
 static void stm32_dfsdm_dma_buffer_done(void *data)
 {
 	struct iio_dev *indio_dev = data;
@@ -874,11 +849,6 @@ static void stm32_dfsdm_dma_buffer_done(void *data)
 	int available = stm32_dfsdm_adc_dma_residue(adc);
 	size_t old_pos;
 
-	if (indio_dev->currentmode & INDIO_BUFFER_TRIGGERED) {
-		iio_trigger_poll_chained(indio_dev->trig);
-		return;
-	}
-
 	/*
 	 * FIXME: In Kernel interface does not support cyclic DMA buffer,and
 	 * offers only an interface to push data samples per samples.
@@ -906,7 +876,15 @@ static void stm32_dfsdm_dma_buffer_done(void *data)
 			adc->bufi = 0;
 			old_pos = 0;
 		}
-		/* regular iio buffer without trigger */
+		/*
+		 * In DMA mode the trigger services of IIO are not used
+		 * (e.g. no call to iio_trigger_poll).
+		 * Calling irq handler associated to the hardware trigger is not
+		 * relevant as the conversions have already been done. Data
+		 * transfers are performed directly in DMA callback instead.
+		 * This implementation avoids to call trigger irq handler that
+		 * may sleep, in an atomic context (DMA irq handler context).
+		 */
 		if (adc->dev_data->type == DFSDM_IIO)
 			iio_push_to_buffers(indio_dev, buffer);
 	}
@@ -1536,8 +1514,7 @@ static int stm32_dfsdm_adc_init(struct iio_dev *indio_dev)
 	}
 
 	ret = iio_triggered_buffer_setup(indio_dev,
-					 &iio_pollfunc_store_time,
-					 &stm32_dfsdm_adc_trigger_handler,
+					 &iio_pollfunc_store_time, NULL,
 					 &stm32_dfsdm_buffer_setup_ops);
 	if (ret) {
 		stm32_dfsdm_dma_release(indio_dev);
-- 
2.17.1