[PATCH RFC] dmaengine: fsl-edma: check channel acquisition before use

dma_get_slave_channel() can return NULL when acquiring a channel fails,
for example if fsl_edma_alloc_chan_resources() cannot request an IRQ.
fsl_edma3_xlate() dereferences that return value to update privatecnt.

Acquire and check the channel before publishing its source ID and
request parameters. A NULL-only check after the existing source-ID
assignment would leave the failed request marked as in use, causing
fsl_edma_srcid_in_use() to reject a subsequent request for that source.
The channel resource-allocation callback does not consume these request
parameters, so set them only after acquisition succeeds. The existing
scoped mutex release and successful-channel return are preserved.

Detected by static analysis and reviewed with AI-assisted source auditing.

Fixes: 72f5801a4e2b ("dmaengine: fsl-edma: integrate v3 support")
Assisted-by: LLM
Signed-off-by: Slavin Liu <redacted>
---
 drivers/dma/fsl-edma-main.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/dma/fsl-edma-main.c b/drivers/dma/fsl-edma-main.c
index d9fb717b5b53..6934ac882697 100644
--- a/drivers/dma/fsl-edma-main.c
+++ b/drivers/dma/fsl-edma-main.c

@@ -326,13 +326,16 @@ static struct dma_chan *fsl_edma3_xlate(struct of_phandle_args *dma_spec,
 		if ((dma_spec->args[2] & FSL_EDMA_ODD_CH) && !(i & 0x1))
 			continue;
 
+		chan = dma_get_slave_channel(chan);
+		if (!chan)
+			return NULL;
+
 		fsl_chan->srcid = dma_spec->args[0];
 		fsl_chan->priority = dma_spec->args[1];
 		fsl_chan->is_rxchan = dma_spec->args[2] & FSL_EDMA_RX;
 		fsl_chan->is_remote = dma_spec->args[2] & FSL_EDMA_REMOTE;
 		fsl_chan->is_multi_fifo = dma_spec->args[2] & FSL_EDMA_MULTI_FIFO;
 
-		chan = dma_get_slave_channel(chan);
 		chan->device->privatecnt++;
 		return chan;
 	}