[PATCH] media: stm32-dcmi: fix DMA corruption when stopping streaming

[Hugues Fruchet <hugues.fruchet@st.com>]

Avoid call of dmaengine_terminate_all() between
dmaengine_prep_slave_single() and dmaengine_submit() by locking
the whole DMA submission sequence.

Signed-off-by: Hugues Fruchet <hugues.fruchet@st.com>
---
 drivers/media/platform/stm32/stm32-dcmi.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/drivers/media/platform/stm32/stm32-dcmi.c b/drivers/media/platform/stm32/stm32-dcmi.c
index f44d8a7..a611a21 100644
--- a/drivers/media/platform/stm32/stm32-dcmi.c
+++ b/drivers/media/platform/stm32/stm32-dcmi.c
@@ -164,6 +164,9 @@ struct stm32_dcmi {
 	int				errors_count;
 	int				overrun_count;
 	int				buffers_count;
+
+	/* Ensure DMA operations atomicity */
+	struct mutex			dma_lock;
 };
 
 static inline struct stm32_dcmi *notifier_to_dcmi(struct v4l2_async_notifier *n)
@@ -314,6 +317,13 @@ static int dcmi_start_dma(struct stm32_dcmi *dcmi,
 		return ret;
 	}
 
+	/*
+	 * Avoid call of dmaengine_terminate_all() between
+	 * dmaengine_prep_slave_single() and dmaengine_submit()
+	 * by locking the whole DMA submission sequence
+	 */
+	mutex_lock(&dcmi->dma_lock);
+
 	/* Prepare a DMA transaction */
 	desc = dmaengine_prep_slave_single(dcmi->dma_chan, buf->paddr,
 					   buf->size,
@@ -322,6 +332,7 @@ static int dcmi_start_dma(struct stm32_dcmi *dcmi,
 	if (!desc) {
 		dev_err(dcmi->dev, "%s: DMA dmaengine_prep_slave_single failed for buffer phy=%pad size=%zu\n",
 			__func__, &buf->paddr, buf->size);
+		mutex_unlock(&dcmi->dma_lock);
 		return -EINVAL;
 	}
 
@@ -333,9 +344,12 @@ static int dcmi_start_dma(struct stm32_dcmi *dcmi,
 	dcmi->dma_cookie = dmaengine_submit(desc);
 	if (dma_submit_error(dcmi->dma_cookie)) {
 		dev_err(dcmi->dev, "%s: DMA submission failed\n", __func__);
+		mutex_unlock(&dcmi->dma_lock);
 		return -ENXIO;
 	}
 
+	mutex_unlock(&dcmi->dma_lock);
+
 	dma_async_issue_pending(dcmi->dma_chan);
 
 	return 0;
@@ -720,7 +734,9 @@ static void dcmi_stop_streaming(struct vb2_queue *vq)
 	spin_unlock_irq(&dcmi->irqlock);
 
 	/* Stop all pending DMA operations */
+	mutex_lock(&dcmi->dma_lock);
 	dmaengine_terminate_all(dcmi->dma_chan);
+	mutex_unlock(&dcmi->dma_lock);
 
 	pm_runtime_put(dcmi->dev);
 
@@ -1711,6 +1727,7 @@ static int dcmi_probe(struct platform_device *pdev)
 
 	spin_lock_init(&dcmi->irqlock);
 	mutex_init(&dcmi->lock);
+	mutex_init(&dcmi->dma_lock);
 	init_completion(&dcmi->complete);
 	INIT_LIST_HEAD(&dcmi->buffers);
 
-- 
2.7.4