dma: axi-dmac: terminate early DMA transfers after a partial one

When we get a partial transfer, we should not submit any more segments to
the hardware, as the data it will get will be unused and will just do
unnecessary processing.

During the start of transfer, we check it there was a partial transfer in a
previous completed segment and add the TLAST flag to the next segment that
is about to be submitted.

Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>

drivers/dma/dma-axi-dmac.c

@@ -105,6 +105,7 @@ struct axi_dmac_sg {
 struct axi_dmac_desc {
 	struct virt_dma_desc vdesc;
 	bool cyclic;
+	bool have_partial_xfer;
 
 	unsigned int num_submitted;
 	unsigned int num_completed;
@@ -234,7 +235,8 @@ static void axi_dmac_start_transfer(struct axi_dmac_chan *chan)
 	}
 
 	desc->num_submitted++;
-	if (desc->num_submitted == desc->num_sgs) {
+	if (desc->num_submitted == desc->num_sgs ||
+	    desc->have_partial_xfer) {
 		if (desc->cyclic) {
 			desc->num_submitted = 0; /* Start again */
 		} else {
@@ -309,6 +311,7 @@ static void axi_dmac_dequeue_partial_xfers(struct axi_dmac_chan *chan)
 				if (sg->id == AXI_DMAC_SG_UNUSED)
 					continue;
 				if (sg->id == id) {
+					desc->have_partial_xfer = true;
 					sg->partial_len = len;
 					found_sg = true;
 					break;