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

When a partial transfer is received, the driver should not submit any more
segments to the hardware, as they will be ignored/unused until a new
transfer start operation is done.

This change implements this by adding a new flag on the AXI DMAC
descriptor. This flags is set to true, if there was a partial transfer in
a previously completed segment. When that flag is true, the TLAST flag is
added to the to the submitted segment, signaling the controller to stop
receiving more segments.

Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Signed-off-by: Vinod Koul <vkoul@kernel.org>

drivers/dma/dma-axi-dmac.c

@@ -96,6 +96,7 @@ 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;
@@ -220,7 +221,8 @@ 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
@@ -294,6 +296,7 @@ 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;