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

[Jonathan Cameron <jic23@kernel.org>]

On Tue, 21 Jan 2020 12:02:56 +0100
Olivier Moysan <olivier.moysan@st.com> wrote:

> 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>
Applied to the fixes-togreg branch of iio.git and marked for stable.

Thanks,

Jonathan

> ---
> 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);