[PATCH 05/17] 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 that the
decision to start work is made against the current value rather than one
observed before a concurrent terminate_all() deconfigured the channel.

Fixes: e63d79d1ffcd ("dmaengine: Add Synopsys eDMA IP core driver")
Signed-off-by: Koichiro Den <den@xxxxxxxxxxxxx>
---
 drivers/dma/dw-edma/dw-edma-core.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/dma/dw-edma/dw-edma-core.c b/drivers/dma/dw-edma/dw-edma-core.c
index 2777dc0b2aed..489f7fe49840 100644
--- a/drivers/dma/dw-edma/dw-edma-core.c
+++ b/drivers/dma/dw-edma/dw-edma-core.c
@@ -177,8 +177,10 @@ dw_edma_device_get_config(struct dma_chan *dchan,
 static int dw_edma_device_pause(struct dma_chan *dchan)
 {
 	struct dw_edma_chan *chan = dchan2dw_edma_chan(dchan);
+	unsigned long flags;
 	int err = 0;
 
+	spin_lock_irqsave(&chan->vc.lock, flags);
 	if (!chan->configured)
 		err = -EPERM;
 	else if (chan->status != EDMA_ST_BUSY)
@@ -187,6 +189,7 @@ static int dw_edma_device_pause(struct dma_chan *dchan)
 		err = -EPERM;
 	else
 		chan->request = EDMA_REQ_PAUSE;
+	spin_unlock_irqrestore(&chan->vc.lock, flags);
 
 	return err;
 }
@@ -194,8 +197,10 @@ static int dw_edma_device_pause(struct dma_chan *dchan)
 static int dw_edma_device_resume(struct dma_chan *dchan)
 {
 	struct dw_edma_chan *chan = dchan2dw_edma_chan(dchan);
+	unsigned long flags;
 	int err = 0;
 
+	spin_lock_irqsave(&chan->vc.lock, flags);
 	if (!chan->configured) {
 		err = -EPERM;
 	} else if (chan->status != EDMA_ST_PAUSE) {
@@ -206,6 +211,7 @@ static int dw_edma_device_resume(struct dma_chan *dchan)
 		chan->status = EDMA_ST_BUSY;
 		dw_edma_start_transfer(chan);
 	}
+	spin_unlock_irqrestore(&chan->vc.lock, flags);
 
 	return err;
 }
@@ -249,11 +255,9 @@ 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