dmaengine: xilinx: xdma: Fix synchronization issue

The current xdma_synchronize method does not properly wait for the last
transfer to be done. Due to limitations of the XMDA engine, it is not
possible to stop a transfer in the middle of a descriptor. Said
otherwise, if a stop is requested at the end of descriptor "N" and the OS
is fast enough, the DMA controller will effectively stop immediately.
However, if the OS is slightly too slow to request the stop and the DMA
engine starts descriptor "N+1", the N+1 transfer will be performed until
its end. This means that after a terminate_all, the last descriptor must
remain valid and the synchronization must wait for this last descriptor to
be terminated.

Fixes: 855c2e1 ("dmaengine: xilinx: xdma: Rework xdma_terminate_all()")
Fixes: f5c392d ("dmaengine: xilinx: xdma: Add terminate_all/synchronize callbacks")
Cc: [email protected]
Suggested-by: Miquel Raynal <[email protected]>
Signed-off-by: Louis Chauvet <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Vinod Koul <[email protected]>

Author: Fomys

drivers/dma/xilinx/xdma-regs.h

@@ -117,6 +117,9 @@ struct xdma_hw_desc {
 			 CHAN_CTRL_IE_WRITE_ERROR |			\
 			 CHAN_CTRL_IE_DESC_ERROR)
 
+/* bits of the channel status register */
+#define XDMA_CHAN_STATUS_BUSY			BIT(0)
+
 #define XDMA_CHAN_STATUS_MASK CHAN_CTRL_START
 
 #define XDMA_CHAN_ERROR_MASK (CHAN_CTRL_IE_DESC_ALIGN_MISMATCH |	\

drivers/dma/xilinx/xdma.c

@@ -71,6 +71,8 @@ struct xdma_chan {
 	enum dma_transfer_direction	dir;
 	struct dma_slave_config		cfg;
 	u32				irq;
+	struct completion		last_interrupt;
+	bool				stop_requested;
 };
 
 /**
@@ -376,6 +378,8 @@ static int xdma_xfer_start(struct xdma_chan *xchan)
 		return ret;
 
 	xchan->busy = true;
+	xchan->stop_requested = false;
+	reinit_completion(&xchan->last_interrupt);
 
 	return 0;
 }
@@ -387,21 +391,14 @@ static int xdma_xfer_start(struct xdma_chan *xchan)
 static int xdma_xfer_stop(struct xdma_chan *xchan)
 {
 	int ret;
-	u32 val;
 	struct xdma_device *xdev = xchan->xdev_hdl;
 
 	/* clear run stop bit to prevent any further auto-triggering */
 	ret = regmap_write(xdev->rmap, xchan->base + XDMA_CHAN_CONTROL_W1C,
 			   CHAN_CTRL_RUN_STOP);
 	if (ret)
 		return ret;
-
-	/* Clear the channel status register */
-	ret = regmap_read(xdev->rmap, xchan->base + XDMA_CHAN_STATUS_RC, &val);
-	if (ret)
-		return ret;
-
-	return 0;
+	return ret;
 }
 
 /**
@@ -474,6 +471,8 @@ static int xdma_alloc_channels(struct xdma_device *xdev,
 		xchan->xdev_hdl = xdev;
 		xchan->base = base + i * XDMA_CHAN_STRIDE;
 		xchan->dir = dir;
+		xchan->stop_requested = false;
+		init_completion(&xchan->last_interrupt);
 
 		ret = xdma_channel_init(xchan);
 		if (ret)
@@ -521,6 +520,7 @@ static int xdma_terminate_all(struct dma_chan *chan)
 	spin_lock_irqsave(&xdma_chan->vchan.lock, flags);
 
 	xdma_chan->busy = false;
+	xdma_chan->stop_requested = true;
 	vd = vchan_next_desc(&xdma_chan->vchan);
 	if (vd) {
 		list_del(&vd->node);
@@ -542,6 +542,13 @@ static int xdma_terminate_all(struct dma_chan *chan)
 static void xdma_synchronize(struct dma_chan *chan)
 {
 	struct xdma_chan *xdma_chan = to_xdma_chan(chan);
+	struct xdma_device *xdev = xdma_chan->xdev_hdl;
+	int st = 0;
+
+	/* If the engine continues running, wait for the last interrupt */
+	regmap_read(xdev->rmap, xdma_chan->base + XDMA_CHAN_STATUS, &st);
+	if (st & XDMA_CHAN_STATUS_BUSY)
+		wait_for_completion_timeout(&xdma_chan->last_interrupt, msecs_to_jiffies(1000));
 
 	vchan_synchronize(&xdma_chan->vchan);
 }
@@ -876,6 +883,9 @@ static irqreturn_t xdma_channel_isr(int irq, void *dev_id)
 	u32 st;
 	bool repeat_tx;
 
+	if (xchan->stop_requested)
+		complete(&xchan->last_interrupt);
+
 	spin_lock(&xchan->vchan.lock);
 
 	/* get submitted request */