dmaengine: dma-axi-dmac: Gracefully terminate SW cyclic transfers

As of now, to terminate a cyclic transfer, one pretty much needs to use
brute force and terminate all transfers with .device_terminate_all().
With this change, when a cyclic transfer terminates (and generates an
EOT interrupt), look at any new pending transfer with the DMA_PREP_LOAD_EOT
flag set. If there is one, the current cyclic transfer is terminated and
the next one is enqueued. If the flag is not set, that transfer is ignored.

Signed-off-by: Nuno Sá <nuno.sa@analog.com>
Link: https://patch.msgid.link/20260303-axi-dac-cyclic-support-v2-4-0db27b4be95a@analog.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>

1 files changed, 33 insertions, 1 deletions

diff --git a/drivers/dma/dma-axi-dmac.c b/drivers/dma/dma-axi-dmac.c
index a47e08d3dbbc..e9814d725322 100644
--- a/drivers/dma/dma-axi-dmac.c
+++ b/drivers/dma/dma-axi-dmac.c
@@ -233,6 +233,11 @@ static struct axi_dmac_desc *axi_dmac_get_next_desc(struct axi_dmac *dmac,
 	struct virt_dma_desc *vdesc;
 	struct axi_dmac_desc *desc;
 
+	/*
+	 * It means a SW cyclic transfer is in place so we should just return
+	 * the same descriptor. SW cyclic transfer termination is handled
+	 * in axi_dmac_transfer_done().
+	 */
 	if (chan->next_desc)
 		return chan->next_desc;
 
@@ -411,6 +416,32 @@ static void axi_dmac_compute_residue(struct axi_dmac_chan *chan,
 	}
 }
 
+static bool axi_dmac_handle_cyclic_eot(struct axi_dmac_chan *chan,
+				       struct axi_dmac_desc *active)
+{
+	struct device *dev = chan_to_axi_dmac(chan)->dma_dev.dev;
+	struct virt_dma_desc *vdesc;
+
+	/* wrap around */
+	active->num_completed = 0;
+
+	vdesc = vchan_next_desc(&chan->vchan);
+	if (!vdesc)
+		return false;
+	if (!(vdesc->tx.flags & DMA_PREP_LOAD_EOT)) {
+		dev_warn(dev, "Discarding non EOT transfer after cyclic\n");
+		list_del(&vdesc->node);
+		return false;
+	}
+
+	/* then let's end the cyclic transfer */
+	chan->next_desc = NULL;
+	list_del(&active->vdesc.node);
+	vchan_cookie_complete(&active->vdesc);
+
+	return true;
+}
+
 static bool axi_dmac_transfer_done(struct axi_dmac_chan *chan,
 	unsigned int completed_transfers)
 {
@@ -458,7 +489,8 @@ static bool axi_dmac_transfer_done(struct axi_dmac_chan *chan,
 			if (active->num_completed == active->num_sgs ||
 			    sg->partial_len) {
 				if (active->cyclic) {
-					active->num_completed = 0; /* wrap around */
+					/* keep start_next as is, if already true... */
+					start_next |= axi_dmac_handle_cyclic_eot(chan, active);
 				} else {
 					list_del(&active->vdesc.node);
 					vchan_cookie_complete(&active->vdesc);