Reading destination and source is pointless. In DEV_TO_MEM transfers
we are only interested in the destination, in MEM_TO_DEV we care about
the source. In MEM_TO_MEM it really does not matter which one you
read.

Remove the extra pointer and select dest/source via a bool.

Reading the src/dst data from an active parameter set in the EDMA
parameter RAM is not reliable, as there might be a concurrent update
from the controller.

But experimentation showed, that a double readout with comparing the
results and a limited loop works nicely. I've actually never found a
case where the loop limit triggered, but we have it there for sanity
reasons. In case it triggers we return -EBUSY and let the caller deal
with it.

Remove the export of this function while at it. The only potential
user is the dmaengine and that's always builtin.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 arch/arm/common/edma.c             |   48 ++++++++++++++++++++++++++-----------
 include/linux/platform_data/edma.h |    2 -
 2 files changed, 35 insertions(+), 15 deletions(-)

Index: linux/arch/arm/common/edma.c
===================================================================
--- linux.orig/arch/arm/common/edma.c
+++ linux/arch/arm/common/edma.c
@@ -994,29 +994,49 @@ void edma_set_dest(unsigned slot, dma_ad
 EXPORT_SYMBOL(edma_set_dest);
 
 /**
- * edma_get_position - returns the current transfer points
+ * edma_get_position - returns the current transfer point
  * @slot: parameter RAM slot being examined
- * @src: pointer to source port position
- * @dst: pointer to destination port position
+ * @pos:  where to store the data
+ * @dst:  true selects the dest position, false the source
  *
- * Returns current source and destination addresses for a particular
- * parameter RAM slot.  Its channel should not be active when this is called.
+ * Return 0 indicates a stable readout. -EBUSY indicates that the
+ * readout failed due to concurrent updates.
+ *
+ * Call this on active channels with care. For inactive channels this
+ * never fails.
  */
-void edma_get_position(unsigned slot, dma_addr_t *src, dma_addr_t *dst)
+int edma_get_position(unsigned slot, dma_addr_t *pos, bool dst)
 {
-	struct edmacc_param temp;
-	unsigned ctlr;
+	u32 dat, ctlr, offs;
+	int i;
 
 	ctlr = EDMA_CTLR(slot);
 	slot = EDMA_CHAN_SLOT(slot);
 
-	edma_read_slot(EDMA_CTLR_CHAN(ctlr, slot), &temp);
-	if (src != NULL)
-		*src = temp.src;
-	if (dst != NULL)
-		*dst = temp.dst;
+	if (slot >= edma_cc[ctlr]->num_slots)
+		return -EINVAL;
+
+	offs = PARM_OFFSET(slot);
+	offs += dst ? PARM_DST : PARM_SRC;
+
+	/*
+	 * If the channel is active, we need to double read as we
+	 * might see half updated data. We limit this to 5
+	 * attempts. If that fails we return -EBUSY and let the caller
+	 * deal with it.
+	 */
+	dat = edma_read(ctlr, offs);
+	for (i = 0; i < 5; i++) {
+		u32 tmp = edma_read(ctlr, offs);
+
+		if (tmp == dat) {
+			*pos = dat;
+			return 0;
+		}
+		dat = tmp;
+	}
+	return -EBUSY;
 }
-EXPORT_SYMBOL(edma_get_position);
 
 /**
  * edma_set_src_index - configure DMA source address indexing
Index: linux/include/linux/platform_data/edma.h
===================================================================
--- linux.orig/include/linux/platform_data/edma.h
+++ linux/include/linux/platform_data/edma.h
@@ -130,7 +130,7 @@ void edma_set_src(unsigned slot, dma_add
 				enum address_mode mode, enum fifo_width);
 void edma_set_dest(unsigned slot, dma_addr_t dest_port,
 				 enum address_mode mode, enum fifo_width);
-void edma_get_position(unsigned slot, dma_addr_t *src, dma_addr_t *dst);
+int __must_check edma_get_position(unsigned slot, dma_addr_t *pos, bool dst);
 void edma_set_src_index(unsigned slot, s16 src_bidx, s16 src_cidx);
 void edma_set_dest_index(unsigned slot, s16 dest_bidx, s16 dest_cidx);
 void edma_set_transfer_params(unsigned slot, u16 acnt, u16 bcnt, u16 ccnt,