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

@@ -471,6 +471,20 @@ static struct at_xdmac_desc *at_xdmac_get_desc(struct at_xdmac_chan *atchan)
 	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 @@ at_xdmac_prep_slave_sg(struct dma_chan *chan, struct scatterlist *sgl,
 		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 @@ at_xdmac_prep_dma_cyclic(struct dma_chan *chan, dma_addr_t buf_addr,
 		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 @@ at_xdmac_prep_dma_cyclic(struct dma_chan *chan, dma_addr_t buf_addr,
 			 __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 @@ at_xdmac_prep_dma_memcpy(struct dma_chan *chan, dma_addr_t dest, dma_addr_t src,
 		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 @@ at_xdmac_prep_dma_memcpy(struct dma_chan *chan, dma_addr_t dest, dma_addr_t src,
 			 __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)