[PATCH] dmaengine: pxa: handle bus errors

[Robert Jarzmik]

In the current state, upon bus error the driver will spin endlessly,
relaunching the last tx, which will fail again and again :
 - a bus error happens
 - pxad_chan_handler() is called
 - as PXA_DCSR_STOPSTATE is true, the last non-terminated transaction is
   lauched, which is the one triggering the bus error, as it didn't
   terminate
 - moreover, the STOP interrupt fires a new, as the STOPIRQEN is still
   active

Break this logic by stopping the automatic relaunch of a dma channel
upon a bus error, even if there are still pending issued requests on it.

As dma_cookie_status() seems unable to return DMA_ERROR in its current
form, ie. there seems no way to mark a DMA_ERROR on a per-async-tx
basis, it is chosen in this patch to remember on the channel which
transaction failed, and report it in pxad_tx_status().

It's a bit misleading because if T1, T2, T3 and T4 were queued, and T1
was completed while T2 causes a bus error, the status of T3 and T4 will
be reported as DMA_IN_PROGRESS, while the channel is actually stopped.

Signed-off-by: Robert Jarzmik <robert.jarzmik at free.fr>
---
 drivers/dma/pxa_dma.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/drivers/dma/pxa_dma.c b/drivers/dma/pxa_dma.c
index debca824bed6..0dc5a528c463 100644
--- a/drivers/dma/pxa_dma.c
+++ b/drivers/dma/pxa_dma.c
@@ -117,6 +117,7 @@ struct pxad_chan {
 	/* protected by vc->lock */
 	struct pxad_phy		*phy;
 	struct dma_pool		*desc_pool;	/* Descriptors pool */
+	dma_cookie_t		bus_error;
 };
 
 struct pxad_device {
@@ -560,6 +561,7 @@ static void pxad_launch_chan(struct pxad_chan *chan,
 			return;
 		}
 	}
+	chan->bus_error = 0;
 
 	/*
 	 * Program the descriptor's address into the DMA controller,
@@ -663,6 +665,7 @@ static irqreturn_t pxad_chan_handler(int irq, void *dev_id)
 	struct virt_dma_desc *vd, *tmp;
 	unsigned int dcsr;
 	unsigned long flags;
+	dma_cookie_t last_started = 0;
 
 	BUG_ON(!chan);
 
@@ -675,6 +678,7 @@ static irqreturn_t pxad_chan_handler(int irq, void *dev_id)
 		dev_dbg(&chan->vc.chan.dev->device,
 			"%s(): checking txd %p[%x]: completed=%d\n",
 			__func__, vd, vd->tx.cookie, is_desc_completed(vd));
+		last_started = vd->tx.cookie;
 		if (to_pxad_sw_desc(vd)->cyclic) {
 			vchan_cyclic_callback(vd);
 			break;
@@ -687,7 +691,12 @@ static irqreturn_t pxad_chan_handler(int irq, void *dev_id)
 		}
 	}
 
-	if (dcsr & PXA_DCSR_STOPSTATE) {
+	if (dcsr & PXA_DCSR_BUSERR) {
+		chan->bus_error = last_started;
+		phy_disable(phy);
+	}
+
+	if (!chan->bus_error && dcsr & PXA_DCSR_STOPSTATE) {
 		dev_dbg(&chan->vc.chan.dev->device,
 		"%s(): channel stopped, submitted_empty=%d issued_empty=%d",
 			__func__,
@@ -1245,6 +1254,9 @@ static enum dma_status pxad_tx_status(struct dma_chan *dchan,
 	struct pxad_chan *chan = to_pxad_chan(dchan);
 	enum dma_status ret;
 
+	if (cookie == chan->bus_error)
+		return DMA_ERROR;
+
 	ret = dma_cookie_status(dchan, cookie, txstate);
 	if (likely(txstate && (ret != DMA_ERROR)))
 		dma_set_residue(txstate, pxad_residue(chan, cookie));
-- 
2.1.4