[PATCH v2 4/4] dmaengine: xilinx: xdma: Add terminate_all/synchronize callbacks

Miquel Raynal
2023-11-30T11:13:20Z

The driver is capable of starting scatter-gather transfers and needs to
wait until their end. It is also capable of starting cyclic transfers
and will only be "reset" next time the channel will be reused. In
practice most of the time we hear no audio glitch because the sound card
stops the flow on its side so the DMA transfers are just
discarded. There are however some cases (when playing a bit with a
number of frames and with a discontinuous sound file) when the sound
card seems to be slightly too slow at stopping the flow, leading to a
glitch that can be heard.

In all cases, we need to earn better control of the DMA engine and
adding proper ->device_terminate_all() and ->device_synchronize()
callbacks feels totally relevant. With these two callbacks, no glitch
can be heard anymore.

Fixes: cd8c732ce1a5 ("dmaengine: xilinx: xdma: Support cyclic transfers")
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
---

This was only tested with cyclic transfers.
---
drivers/dma/xilinx/xdma.c | 68 +++++++++++++++++++++++++++++++++++++++
1 file changed, 68 insertions(+)

diff --git a/drivers/dma/xilinx/xdma.c b/drivers/dma/xilinx/xdma.c
index e931ff42209c..290bb5d2d1e2 100644
--- a/drivers/dma/xilinx/xdma.c
+++ b/drivers/dma/xilinx/xdma.c
@@ -371,6 +371,31 @@ static int xdma_xfer_start(struct xdma_chan *xchan)
return ret;

xchan->busy = true;
+
+ return 0;
+}
+
+/**
+ * xdma_xfer_stop - Stop DMA transfer
+ * @xchan: DMA channel pointer
+ */
+static int xdma_xfer_stop(struct xdma_chan *xchan)
+{
+ struct virt_dma_desc *vd = vchan_next_desc(&xchan->vchan);
+ struct xdma_device *xdev = xchan->xdev_hdl;
+ int ret;
+
+ if (!vd || !xchan->busy)
+ return -EINVAL;
+
+ /* clear run stop bit to prevent any further auto-triggering */
+ ret = regmap_write(xdev->rmap, xchan->base + XDMA_CHAN_CONTROL_W1C,
+ CHAN_CTRL_RUN_STOP);
+ if (ret)
+ return ret;
+
+ xchan->busy = false;
+
return 0;
}

@@ -475,6 +500,47 @@ static void xdma_issue_pending(struct dma_chan *chan)
spin_unlock_irqrestore(&xdma_chan->vchan.lock, flags);
}

+/**
+ * xdma_terminate_all - Terminate all transactions
+ * @chan: DMA channel pointer
+ */
+static int xdma_terminate_all(struct dma_chan *chan)
+{
+ struct xdma_chan *xdma_chan = to_xdma_chan(chan);
+ struct xdma_desc *desc = NULL;
+ struct virt_dma_desc *vd;
+ unsigned long flags;
+ LIST_HEAD(head);
+
+ spin_lock_irqsave(&xdma_chan->vchan.lock, flags);
+ xdma_xfer_stop(xdma_chan);
+
+ vd = vchan_next_desc(&xdma_chan->vchan);
+ if (vd)
+ desc = to_xdma_desc(vd);
+ if (desc) {
+ dma_cookie_complete(&desc->vdesc.tx);
+ vchan_terminate_vdesc(&desc->vdesc);
+ }
+
+ vchan_get_all_descriptors(&xdma_chan->vchan, &head);
+ spin_unlock_irqrestore(&xdma_chan->vchan.lock, flags);
+ vchan_dma_desc_free_list(&xdma_chan->vchan, &head);
+
+ return 0;
+}
+
+/**
+ * xdma_synchronize - Synchronize terminated transactions
+ * @chan: DMA channel pointer
+ */
+static void xdma_synchronize(struct dma_chan *chan)
+{
+ struct xdma_chan *xdma_chan = to_xdma_chan(chan);
+
+ vchan_synchronize(&xdma_chan->vchan);
+}
+
/**
* xdma_prep_device_sg - prepare a descriptor for a DMA transaction
* @chan: DMA channel pointer
@@ -1088,6 +1154,8 @@ static int xdma_probe(struct platform_device *pdev)
xdev->dma_dev.device_prep_slave_sg = xdma_prep_device_sg;
xdev->dma_dev.device_config = xdma_device_config;
xdev->dma_dev.device_issue_pending = xdma_issue_pending;
+ xdev->dma_dev.device_terminate_all = xdma_terminate_all;
+ xdev->dma_dev.device_synchronize = xdma_synchronize;
xdev->dma_dev.filter.map = pdata->device_map;
xdev->dma_dev.filter.mapcnt = pdata->device_map_cnt;
xdev->dma_dev.filter.fn = xdma_filter_fn;
--
2.34.1