iio: adc: stm32-dfsdm: add comment for 16 bits record

Add a comment on DMA configuration for 16 bits record.

Signed-off-by: Olivier Moysan <olivier.moysan@st.com>
Acked-by: Fabrice Gasnier <fabrice.gasnier@st.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

diff --git a/drivers/iio/adc/stm32-dfsdm-adc.c b/drivers/iio/adc/stm32-dfsdm-adc.c
index d855a60..ee1e056 100644 (file)
--- a/drivers/iio/adc/stm32-dfsdm-adc.c
+++ b/drivers/iio/adc/stm32-dfsdm-adc.c
@@ -918,6 +918,11 @@ static void stm32_dfsdm_dma_buffer_done(void *data)
 static int stm32_dfsdm_adc_dma_start(struct iio_dev *indio_dev)
 {
        struct stm32_dfsdm_adc *adc = iio_priv(indio_dev);
+       /*
+        * The DFSDM supports half-word transfers. However, for 16 bits record,
+        * 4 bytes buswidth is kept, to avoid losing samples LSBs when left
+        * shift is required.
+        */
        struct dma_slave_config config = {
                .src_addr = (dma_addr_t)adc->dfsdm->phys_base,
                .src_addr_width = DMA_SLAVE_BUSWIDTH_4_BYTES,