linux-kernel - [PATCH 5/5] iio: adc: stm32-dfsdm: add comment for 16 bits record

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Message-ID: <1560949431-22948-6-git-send-email-olivier.moysan@st.com>
Date:   Wed, 19 Jun 2019 15:03:51 +0200
From:   Olivier Moysan <olivier.moysan@...com>
To:     <jic23@...nel.org>, <knaack.h@....de>, <lars@...afoo.de>,
        <pmeerw@...erw.net>, <mcoquelin.stm32@...il.com>,
        <alexandre.torgue@...com>, <fabrice.gasnier@...com>,
        <linux-iio@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <benjamin.gaignard@...com>,
        <olivier.moysan@...com>
Subject: [PATCH 5/5] 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@...com>
---
 drivers/iio/adc/stm32-dfsdm-adc.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/iio/adc/stm32-dfsdm-adc.c b/drivers/iio/adc/stm32-dfsdm-adc.c
index d855a605eab6..ee1e0569d0e1 100644
--- 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,
-- 
2.7.4