dmaengine: stm32-mdma: correct desc prep when channel running

In case of the prep descriptor while the channel is already running, the
CCR register value stored into the channel could already have its EN bit
set.  This would lead to a bad transfer since, at start transfer time,
enabling the channel while other registers aren't yet properly set.
To avoid this, ensure to mask the CCR_EN bit when storing the ccr value
into the mdma channel structure.

Fixes: a4ffb13 ("dmaengine: Add STM32 MDMA driver")
Signed-off-by: Alain Volmat <alain.volmat@foss.st.com>
Signed-off-by: Amelie Delaunay <amelie.delaunay@foss.st.com>
Cc: stable@vger.kernel.org
Tested-by: Alain Volmat <alain.volmat@foss.st.com>
Link: https://lore.kernel.org/r/20231009082450.452877-1-amelie.delaunay@foss.st.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>

Author: Alain Volmat

drivers/dma/stm32-mdma.c

@@ -488,7 +488,7 @@ static int stm32_mdma_set_xfer_param(struct stm32_mdma_chan *chan,
 	src_maxburst = chan->dma_config.src_maxburst;
 	dst_maxburst = chan->dma_config.dst_maxburst;
 
-	ccr = stm32_mdma_read(dmadev, STM32_MDMA_CCR(chan->id));
+	ccr = stm32_mdma_read(dmadev, STM32_MDMA_CCR(chan->id)) & ~STM32_MDMA_CCR_EN;
 	ctcr = stm32_mdma_read(dmadev, STM32_MDMA_CTCR(chan->id));
 	ctbr = stm32_mdma_read(dmadev, STM32_MDMA_CTBR(chan->id));
 
@@ -966,7 +966,7 @@ stm32_mdma_prep_dma_memcpy(struct dma_chan *c, dma_addr_t dest, dma_addr_t src,
 	if (!desc)
 		return NULL;
 
-	ccr = stm32_mdma_read(dmadev, STM32_MDMA_CCR(chan->id));
+	ccr = stm32_mdma_read(dmadev, STM32_MDMA_CCR(chan->id)) & ~STM32_MDMA_CCR_EN;
 	ctcr = stm32_mdma_read(dmadev, STM32_MDMA_CTCR(chan->id));
 	ctbr = stm32_mdma_read(dmadev, STM32_MDMA_CTBR(chan->id));
 	cbndtr = stm32_mdma_read(dmadev, STM32_MDMA_CBNDTR(chan->id));