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-rw-r--r--drivers/dma/edma.c41
1 files changed, 40 insertions, 1 deletions
diff --git a/drivers/dma/edma.c b/drivers/dma/edma.c
index d92d655..e3d7fcb 100644
--- a/drivers/dma/edma.c
+++ b/drivers/dma/edma.c
@@ -113,6 +113,9 @@
#define GET_NUM_REGN(x) ((x & 0x300000) >> 20) /* bits 20-21 */
#define CHMAP_EXIST BIT(24)
+/* CCSTAT register */
+#define EDMA_CCSTAT_ACTV BIT(4)
+
/*
* Max of 20 segments per channel to conserve PaRAM slots
* Also note that MAX_NR_SG should be atleast the no.of periods
@@ -1680,9 +1683,20 @@ static void edma_issue_pending(struct dma_chan *chan)
spin_unlock_irqrestore(&echan->vchan.lock, flags);
}
+/*
+ * This limit exists to avoid a possible infinite loop when waiting for proof
+ * that a particular transfer is completed. This limit can be hit if there
+ * are large bursts to/from slow devices or the CPU is never able to catch
+ * the DMA hardware idle. On an AM335x transfering 48 bytes from the UART
+ * RX-FIFO, as many as 55 loops have been seen.
+ */
+#define EDMA_MAX_TR_WAIT_LOOPS 1000
+
static u32 edma_residue(struct edma_desc *edesc)
{
bool dst = edesc->direction == DMA_DEV_TO_MEM;
+ int loop_count = EDMA_MAX_TR_WAIT_LOOPS;
+ struct edma_chan *echan = edesc->echan;
struct edma_pset *pset = edesc->pset;
dma_addr_t done, pos;
int i;
@@ -1691,7 +1705,32 @@ static u32 edma_residue(struct edma_desc *edesc)
* We always read the dst/src position from the first RamPar
* pset. That's the one which is active now.
*/
- pos = edma_get_position(edesc->echan->ecc, edesc->echan->slot[0], dst);
+ pos = edma_get_position(echan->ecc, echan->slot[0], dst);
+
+ /*
+ * "pos" may represent a transfer request that is still being
+ * processed by the EDMACC or EDMATC. We will busy wait until
+ * any one of the situations occurs:
+ * 1. the DMA hardware is idle
+ * 2. a new transfer request is setup
+ * 3. we hit the loop limit
+ */
+ while (edma_read(echan->ecc, EDMA_CCSTAT) & EDMA_CCSTAT_ACTV) {
+ /* check if a new transfer request is setup */
+ if (edma_get_position(echan->ecc,
+ echan->slot[0], dst) != pos) {
+ break;
+ }
+
+ if (!--loop_count) {
+ dev_dbg_ratelimited(echan->vchan.chan.device->dev,
+ "%s: timeout waiting for PaRAM update\n",
+ __func__);
+ break;
+ }
+
+ cpu_relax();
+ }
/*
* Cyclic is simple. Just subtract pset[0].addr from pos.
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