dmaengine: at_xdmac: Move the free desc to the tail of the desc list

Move the free desc to the tail of the list, so that the sequence of
descriptors is more track-able in case of debug. One would know which
descriptor should come next and could easier catch concurrency over
descriptors for example. virt-dma uses list_splice_tail_init() as well,
follow the core driver.

Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Link: https://lore.kernel.org/r/20211215110115.191749-7-tudor.ambarus@microchip.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>

drivers/dma/at_xdmac.c

@@ -729,7 +729,8 @@ at_xdmac_prep_slave_sg(struct dma_chan *chan, struct scatterlist *sgl,
 		if (!desc) {
 			dev_err(chan2dev(chan), "can't get descriptor\n");
 			if (first)
-				list_splice_init(&first->descs_list, &atchan->free_descs_list);
+				list_splice_tail_init(&first->descs_list,
+						      &atchan->free_descs_list);
 			goto spin_unlock;
 		}
 
@@ -817,7 +818,8 @@ at_xdmac_prep_dma_cyclic(struct dma_chan *chan, dma_addr_t buf_addr,
 		if (!desc) {
 			dev_err(chan2dev(chan), "can't get descriptor\n");
 			if (first)
-				list_splice_init(&first->descs_list, &atchan->free_descs_list);
+				list_splice_tail_init(&first->descs_list,
+						      &atchan->free_descs_list);
 			spin_unlock_irqrestore(&atchan->lock, irqflags);
 			return NULL;
 		}
@@ -1051,8 +1053,8 @@ at_xdmac_prep_interleaved(struct dma_chan *chan,
 							       src_addr, dst_addr,
 							       xt, chunk);
 			if (!desc) {
-				list_splice_init(&first->descs_list,
-						 &atchan->free_descs_list);
+				list_splice_tail_init(&first->descs_list,
+						      &atchan->free_descs_list);
 				return NULL;
 			}
 
@@ -1132,7 +1134,8 @@ at_xdmac_prep_dma_memcpy(struct dma_chan *chan, dma_addr_t dest, dma_addr_t src,
 		if (!desc) {
 			dev_err(chan2dev(chan), "can't get descriptor\n");
 			if (first)
-				list_splice_init(&first->descs_list, &atchan->free_descs_list);
+				list_splice_tail_init(&first->descs_list,
+						      &atchan->free_descs_list);
 			return NULL;
 		}
 
@@ -1308,8 +1311,8 @@ at_xdmac_prep_dma_memset_sg(struct dma_chan *chan, struct scatterlist *sgl,
 						   sg_dma_len(sg),
 						   value);
 		if (!desc && first)
-			list_splice_init(&first->descs_list,
-					 &atchan->free_descs_list);
+			list_splice_tail_init(&first->descs_list,
+					      &atchan->free_descs_list);
 
 		if (!first)
 			first = desc;
@@ -1701,7 +1704,8 @@ static void at_xdmac_tasklet(struct tasklet_struct *t)
 
 		spin_lock_irq(&atchan->lock);
 		/* Move the xfer descriptors into the free descriptors list. */
-		list_splice_init(&desc->descs_list, &atchan->free_descs_list);
+		list_splice_tail_init(&desc->descs_list,
+				      &atchan->free_descs_list);
 		at_xdmac_advance_work(atchan);
 		spin_unlock_irq(&atchan->lock);
 	}
@@ -1850,7 +1854,8 @@ static int at_xdmac_device_terminate_all(struct dma_chan *chan)
 	/* Cancel all pending transfers. */
 	list_for_each_entry_safe(desc, _desc, &atchan->xfers_list, xfer_node) {
 		list_del(&desc->xfer_node);
-		list_splice_init(&desc->descs_list, &atchan->free_descs_list);
+		list_splice_tail_init(&desc->descs_list,
+				      &atchan->free_descs_list);
 	}
 
 	clear_bit(AT_XDMAC_CHAN_IS_PAUSED, &atchan->status);