dmaengine: xdmac: Rework the chaining logic

So far, we were setting the NDE bit in our descriptors through some logic to
try to see if we were the last descriptor in the chain.

However, that was turning out to be rather complex to get right, while this
information is also available when we actually chain a new descriptor after an
already existing one.

Simplify this by never setting NDE unless when we actually chain a descriptor.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Acked-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

drivers/dma/at_xdmac.c

diff --git a/drivers/dma/at_xdmac.c b/drivers/dma/at_xdmac.c
index cbeadee..0144a93 100644
--- a/drivers/dma/at_xdmac.c
+++ b/drivers/dma/at_xdmac.c
@@ -471,6 +471,20 @@
 	return desc;
 }
 
+static void at_xdmac_queue_desc(struct dma_chan *chan,
+				struct at_xdmac_desc *prev,
+				struct at_xdmac_desc *desc)
+{
+	if (!prev || !desc)
+		return;
+
+	prev->lld.mbr_nda = desc->tx_dma_desc.phys;
+	prev->lld.mbr_ubc |= AT_XDMAC_MBR_UBC_NDE;
+
+	dev_dbg(chan2dev(chan),	"%s: chain lld: prev=0x%p, mbr_nda=%pad\n",
+		__func__, prev, &prev->lld.mbr_nda);
+}
+
 static struct dma_chan *at_xdmac_xlate(struct of_phandle_args *dma_spec,
 				       struct of_dma *of_dma)
 {
@@ -627,19 +641,14 @@
 		desc->lld.mbr_ubc = AT_XDMAC_MBR_UBC_NDV2			/* next descriptor view */
 			| AT_XDMAC_MBR_UBC_NDEN					/* next descriptor dst parameter update */
 			| AT_XDMAC_MBR_UBC_NSEN					/* next descriptor src parameter update */
-			| (i == sg_len - 1 ? 0 : AT_XDMAC_MBR_UBC_NDE)		/* descriptor fetch */
 			| (len >> fixed_dwidth);				/* microblock length */
 		dev_dbg(chan2dev(chan),
 			 "%s: lld: mbr_sa=%pad, mbr_da=%pad, mbr_ubc=0x%08x\n",
 			 __func__, &desc->lld.mbr_sa, &desc->lld.mbr_da, desc->lld.mbr_ubc);
 
 		/* Chain lld. */
-		if (prev) {
-			prev->lld.mbr_nda = desc->tx_dma_desc.phys;
-			dev_dbg(chan2dev(chan),
-				 "%s: chain lld: prev=0x%p, mbr_nda=%pad\n",
-				 __func__, prev, &prev->lld.mbr_nda);
-		}
+		if (prev)
+			at_xdmac_queue_desc(chan, prev, desc);
 
 		prev = desc;
 		if (!first)
@@ -714,7 +723,6 @@
 		desc->lld.mbr_ubc = AT_XDMAC_MBR_UBC_NDV1
 			| AT_XDMAC_MBR_UBC_NDEN
 			| AT_XDMAC_MBR_UBC_NSEN
-			| AT_XDMAC_MBR_UBC_NDE
 			| period_len >> at_xdmac_get_dwidth(desc->lld.mbr_cfg);
 
 		dev_dbg(chan2dev(chan),
@@ -722,12 +730,8 @@
 			 __func__, &desc->lld.mbr_sa, &desc->lld.mbr_da, desc->lld.mbr_ubc);
 
 		/* Chain lld. */
-		if (prev) {
-			prev->lld.mbr_nda = desc->tx_dma_desc.phys;
-			dev_dbg(chan2dev(chan),
-				 "%s: chain lld: prev=0x%p, mbr_nda=%pad\n",
-				 __func__, prev, &prev->lld.mbr_nda);
-		}
+		if (prev)
+			at_xdmac_queue_desc(chan, prev, desc);
 
 		prev = desc;
 		if (!first)
@@ -850,7 +854,6 @@
 		desc->lld.mbr_ubc = AT_XDMAC_MBR_UBC_NDV2
 			| AT_XDMAC_MBR_UBC_NDEN
 			| AT_XDMAC_MBR_UBC_NSEN
-			| (remaining_size ? AT_XDMAC_MBR_UBC_NDE : 0)
 			| ublen;
 		desc->lld.mbr_cfg = chan_cc;
 
@@ -859,12 +862,8 @@
 			 __func__, &desc->lld.mbr_sa, &desc->lld.mbr_da, desc->lld.mbr_ubc, desc->lld.mbr_cfg);
 
 		/* Chain lld. */
-		if (prev) {
-			prev->lld.mbr_nda = desc->tx_dma_desc.phys;
-			dev_dbg(chan2dev(chan),
-				 "%s: chain lld: prev=0x%p, mbr_nda=0x%08x\n",
-				 __func__, prev, prev->lld.mbr_nda);
-		}
+		if (prev)
+			at_xdmac_queue_desc(chan, prev, desc);
 
 		prev = desc;
 		if (!first)