[PATCH v2] iio: adc: stm32-adc: fix sleep in atomic context

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

This commit fixes the following error:
"BUG: sleeping function called from invalid context at kernel/irq/chip.c"

In DMA mode suppress the trigger irq handler, and make the buffer
transfers directly in DMA callback, instead.

Fixes: 2763ea0585c9 ("iio: adc: stm32: add optional dma support")

Signed-off-by: Olivier Moysan <olivier.moysan@st.com>
---
Changes in v2:
- Add "Fixes" tag in commit message

This solution has been already discussed in the thread
https://lkml.org/lkml/2019/3/30/171, and applied in STM32 DFSDM driver:
e19ac9d9a978 ("iio: adc: stm32-dfsdm: fix sleep in atomic context")
---
 drivers/iio/adc/stm32-adc.c | 31 ++++++++++++++++++++++++++++---
 1 file changed, 28 insertions(+), 3 deletions(-)

diff --git a/drivers/iio/adc/stm32-adc.c b/drivers/iio/adc/stm32-adc.c
index 80c3f963527b..ae622ee6d08c 100644
--- a/drivers/iio/adc/stm32-adc.c
+++ b/drivers/iio/adc/stm32-adc.c
@@ -1418,8 +1418,30 @@ static unsigned int stm32_adc_dma_residue(struct stm32_adc *adc)
 static void stm32_adc_dma_buffer_done(void *data)
 {
 	struct iio_dev *indio_dev = data;
+	struct stm32_adc *adc = iio_priv(indio_dev);
+	int residue = stm32_adc_dma_residue(adc);
+
+	/*
+	 * 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).
+	 */
+	dev_dbg(&indio_dev->dev, "%s bufi=%d\n", __func__, adc->bufi);
 
-	iio_trigger_poll_chained(indio_dev->trig);
+	while (residue >= indio_dev->scan_bytes) {
+		u16 *buffer = (u16 *)&adc->rx_buf[adc->bufi];
+
+		iio_push_to_buffers(indio_dev, buffer);
+
+		residue -= indio_dev->scan_bytes;
+		adc->bufi += indio_dev->scan_bytes;
+		if (adc->bufi >= adc->rx_buf_sz)
+			adc->bufi = 0;
+	}
 }
 
 static int stm32_adc_dma_start(struct iio_dev *indio_dev)
@@ -1845,6 +1867,7 @@ static int stm32_adc_probe(struct platform_device *pdev)
 {
 	struct iio_dev *indio_dev;
 	struct device *dev = &pdev->dev;
+	irqreturn_t (*handler)(int irq, void *p) = NULL;
 	struct stm32_adc *adc;
 	int ret;
 
@@ -1911,9 +1934,11 @@ static int stm32_adc_probe(struct platform_device *pdev)
 	if (ret < 0)
 		return ret;
 
+	if (!adc->dma_chan)
+		handler = &stm32_adc_trigger_handler;
+
 	ret = iio_triggered_buffer_setup(indio_dev,
-					 &iio_pollfunc_store_time,
-					 &stm32_adc_trigger_handler,
+					 &iio_pollfunc_store_time, handler,
 					 &stm32_adc_buffer_setup_ops);
 	if (ret) {
 		dev_err(&pdev->dev, "buffer setup failed\n");
-- 
2.17.1