dmaengine: xilinx: xdma: Fix synchronization issue

The current xdma_synchronize method does not properly wait for the last
transfer to be done. Due to limitations of the XMDA engine, it is not
possible to stop a transfer in the middle of a descriptor. Said
otherwise, if a stop is requested at the end of descriptor "N" and the OS
is fast enough, the DMA controller will effectively stop immediately.
However, if the OS is slightly too slow to request the stop and the DMA
engine starts descriptor "N+1", the N+1 transfer will be performed until
its end. This means that after a terminate_all, the last descriptor must
remain valid and the synchronization must wait for this last descriptor to
be terminated.

Fixes: 855c2e1d1842 ("dmaengine: xilinx: xdma: Rework xdma_terminate_all()")
Fixes: f5c392d106e7 ("dmaengine: xilinx: xdma: Add terminate_all/synchronize callbacks")
Cc: stable@vger.kernel.org
Suggested-by: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: Louis Chauvet <louis.chauvet@bootlin.com>
Link: https://lore.kernel.org/r/20240327-digigram-xdma-fixes-v1-2-45f4a52c0283@bootlin.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>

diff --git a/drivers/dma/xilinx/xdma-regs.h b/drivers/dma/xilinx/xdma-regs.h
index 98f5f6fb9ff9c771270c64c364265f72fd7b216d..6ad08878e93862b770febb71b8bc85e66813428e 100644 (file)
--- a/drivers/dma/xilinx/xdma-regs.h
+++ b/drivers/dma/xilinx/xdma-regs.h
@@ -117,6 +117,9 @@ struct xdma_hw_desc {
                         CHAN_CTRL_IE_WRITE_ERROR |                     \
                         CHAN_CTRL_IE_DESC_ERROR)
 
+/* bits of the channel status register */
+#define XDMA_CHAN_STATUS_BUSY                  BIT(0)
+
 #define XDMA_CHAN_STATUS_MASK CHAN_CTRL_START
 
 #define XDMA_CHAN_ERROR_MASK (CHAN_CTRL_IE_DESC_ALIGN_MISMATCH |       \

diff --git a/drivers/dma/xilinx/xdma.c b/drivers/dma/xilinx/xdma.c
index b9788aa8f6b7b599c6978bce6f58769a7c3f324f..5a3a3293b21b50eca5a141c930ee83fbc11fdae7 100644 (file)
--- a/drivers/dma/xilinx/xdma.c
+++ b/drivers/dma/xilinx/xdma.c
@@ -71,6 +71,8 @@ struct xdma_chan {
        enum dma_transfer_direction     dir;
        struct dma_slave_config         cfg;
        u32                             irq;
+       struct completion               last_interrupt;
+       bool                            stop_requested;
 };
 
 /**
@@ -376,6 +378,8 @@ static int xdma_xfer_start(struct xdma_chan *xchan)
                return ret;
 
        xchan->busy = true;
+       xchan->stop_requested = false;
+       reinit_completion(&xchan->last_interrupt);
 
        return 0;
 }
@@ -387,7 +391,6 @@ static int xdma_xfer_start(struct xdma_chan *xchan)
 static int xdma_xfer_stop(struct xdma_chan *xchan)
 {
        int ret;
-       u32 val;
        struct xdma_device *xdev = xchan->xdev_hdl;
 
        /* clear run stop bit to prevent any further auto-triggering */
@@ -395,13 +398,7 @@ static int xdma_xfer_stop(struct xdma_chan *xchan)
                           CHAN_CTRL_RUN_STOP);
        if (ret)
                return ret;
-
-       /* Clear the channel status register */
-       ret = regmap_read(xdev->rmap, xchan->base + XDMA_CHAN_STATUS_RC, &val);
-       if (ret)
-               return ret;
-
-       return 0;
+       return ret;
 }
 
 /**
@@ -474,6 +471,8 @@ static int xdma_alloc_channels(struct xdma_device *xdev,
                xchan->xdev_hdl = xdev;
                xchan->base = base + i * XDMA_CHAN_STRIDE;
                xchan->dir = dir;
+               xchan->stop_requested = false;
+               init_completion(&xchan->last_interrupt);
 
                ret = xdma_channel_init(xchan);
                if (ret)
@@ -521,6 +520,7 @@ static int xdma_terminate_all(struct dma_chan *chan)
        spin_lock_irqsave(&xdma_chan->vchan.lock, flags);
 
        xdma_chan->busy = false;
+       xdma_chan->stop_requested = true;
        vd = vchan_next_desc(&xdma_chan->vchan);
        if (vd) {
                list_del(&vd->node);
@@ -542,6 +542,13 @@ static int xdma_terminate_all(struct dma_chan *chan)
 static void xdma_synchronize(struct dma_chan *chan)
 {
        struct xdma_chan *xdma_chan = to_xdma_chan(chan);
+       struct xdma_device *xdev = xdma_chan->xdev_hdl;
+       int st = 0;
+
+       /* If the engine continues running, wait for the last interrupt */
+       regmap_read(xdev->rmap, xdma_chan->base + XDMA_CHAN_STATUS, &st);
+       if (st & XDMA_CHAN_STATUS_BUSY)
+               wait_for_completion_timeout(&xdma_chan->last_interrupt, msecs_to_jiffies(1000));
 
        vchan_synchronize(&xdma_chan->vchan);
 }
@@ -876,6 +883,9 @@ static irqreturn_t xdma_channel_isr(int irq, void *dev_id)
        u32 st;
        bool repeat_tx;
 
+       if (xchan->stop_requested)
+               complete(&xchan->last_interrupt);
+
        spin_lock(&xchan->vchan.lock);
 
        /* get submitted request */