Merge tag 'dmaengine-4.6-rc1' of git://git.infradead.org/users/vkoul/slave-dma

[cascardo/linux.git] / drivers / dma / edma.c

diff --git a/drivers/dma/edma.c b/drivers/dma/edma.c
index 29a7723..ee3463e 100644 (file)
--- 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
@@ -1687,9 +1690,20 @@ 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;
@@ -1698,7 +1712,32 @@ 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.