[PATCH v4 5/9] dmaengine: dw-edma: Serialize channel state checks

[Koichiro Den]

pause() and resume() read and update channel state without holding vc.lock,
while the interrupt handlers update the same state under it. Take the same
lock around those state checks so that request, status, and configured stay
consistent.

For example, pause() can observe EDMA_ST_BUSY right before the interrupt
handler completes the final descriptor and moves the channel to
EDMA_ST_IDLE, and then record EDMA_REQ_PAUSE on an already idle channel. No
further interrupt will acknowledge the request, and since issue_pending()
requires EDMA_REQ_NONE, the channel is wedged for good: terminate_all()
leaves the stale request behind, so even reconfiguring the channel does not
recover it.

issue_pending() already runs under vc.lock, but it tests configured before
taking it. Move that test under the lock as well, so configured, request,
and status are evaluated as one channel-state snapshot.

Fixes: e63d79d1ffcd ("dmaengine: Add Synopsys eDMA IP core driver")
Reviewed-by: Frank Li <Frank.Li@xxxxxxx>
Signed-off-by: Koichiro Den <den@xxxxxxxxxxxxx>
---
Changes in v4:
  - Use guard() where lock/unlock is newly added. (Frank)

 drivers/dma/dw-edma/dw-edma-core.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/dma/dw-edma/dw-edma-core.c b/drivers/dma/dw-edma/dw-edma-core.c
index ac40a832a9c7..64ace6b9ebdc 100644
--- a/drivers/dma/dw-edma/dw-edma-core.c
+++ b/drivers/dma/dw-edma/dw-edma-core.c
@@ -302,6 +302,8 @@ static int dw_edma_device_pause(struct dma_chan *dchan)
 	struct dw_edma_chan *chan = dchan2dw_edma_chan(dchan);
 	int err = 0;
 
+	guard(spinlock_irqsave)(&chan->vc.lock);
+
 	if (!chan->configured)
 		err = -EPERM;
 	else if (chan->status != EDMA_ST_BUSY)
@@ -319,6 +321,8 @@ static int dw_edma_device_resume(struct dma_chan *dchan)
 	struct dw_edma_chan *chan = dchan2dw_edma_chan(dchan);
 	int err = 0;
 
+	guard(spinlock_irqsave)(&chan->vc.lock);
+
 	if (!chan->configured) {
 		err = -EPERM;
 	} else if (chan->status != EDMA_ST_PAUSE) {
@@ -369,11 +373,9 @@ static void dw_edma_device_issue_pending(struct dma_chan *dchan)
 	struct dw_edma_chan *chan = dchan2dw_edma_chan(dchan);
 	unsigned long flags;
 
-	if (!chan->configured)
-		return;
-
 	spin_lock_irqsave(&chan->vc.lock, flags);
-	if (vchan_issue_pending(&chan->vc) && chan->request == EDMA_REQ_NONE &&
+	if (chan->configured && vchan_issue_pending(&chan->vc) &&
+	    chan->request == EDMA_REQ_NONE &&
 	    chan->status == EDMA_ST_IDLE) {
 		chan->status = EDMA_ST_BUSY;
 		dw_edma_start_transfer(chan);
-- 
2.51.0