Re: [PATCH v3 7/9] dmaengine: sun6i: track paused virtual channels

[Frank Li <Frank.li@oss.nxp.com>]

On Fri, Oct 23, 2026 at 05:38:26PM -0600, James Hilliard wrote:
> sun6i_dma_tx_status() only returns the cookie state, so a paused but
> incomplete transfer is reported as DMA_IN_PROGRESS. The 8250 RX flush
> path pauses the channel and calls its completion helper before terminating
> it. That helper ignores an in-progress transfer to avoid consuming a new
> RX operation. With sun6i it consequently drops the partial buffer and
> leaves rx_running set, preventing another receive from being submitted.
>
> Track pause state under the channel-assignment lock and report DMA_PAUSED
> for incomplete cookies, including status queries without a residue output.
> Flush the hardware pause request before returning. Completed cookies
> remain DMA_COMPLETE.
>
> Keep paused channels out of the pending queue and do not start a queued
> descriptor when a paused channel's previous descriptor completes. Release
> the completed physical channel so other virtual channels can use it, and
> clear its hardware pause request before reassignment. The paused virtual
> channel retains its queued descriptors until resume.
>
> Resume requeues an unassigned channel only once and schedules the
> allocator, so an idle controller does not require an unrelated completion
> to resume it. Clear the pause state when terminating the channel.
>
> Fixes: 555859308723 ("dmaengine: sun6i: Add driver for the Allwinner A31 DMA controller")
> Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
> ---
>  drivers/dma/sun6i-dma.c | 18 +++++++++++++++---
>  1 file changed, 15 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/dma/sun6i-dma.c b/drivers/dma/sun6i-dma.c
> index dab17b3863fc..25987f550707 100644
> --- a/drivers/dma/sun6i-dma.c
> +++ b/drivers/dma/sun6i-dma.c
> @@ -208,6 +208,7 @@ struct sun6i_vchan {
>  	u8			port;
>  	u8			irq_type;
>  	bool			cyclic;
> +	bool			paused;
>  };
>
>  struct sun6i_dma_dev {
> @@ -537,13 +538,17 @@ static void sun6i_dma_tasklet(struct tasklet_struct *t)
>  		pchan = vchan->phy;
>
>  		if (pchan && !pchan->desc) {
> -			if (sun6i_dma_start_desc(vchan)) {
> +			if (vchan->paused || sun6i_dma_start_desc(vchan)) {
>  				/*
>  				 * No current txd associated with this channel
>  				 */
>  				dev_dbg(sdev->slave.dev, "pchan %u: free\n",
>  					pchan->idx);
>
> +				/* The next owner must not inherit the pause request. */
> +				writel(DMA_CHAN_PAUSE_RESUME,
> +				       pchan->base + DMA_CHAN_PAUSE);
> +
>  				/* Mark this channel free */
>  				vchan->phy = NULL;
>  				pchan->vchan = NULL;
> @@ -935,10 +940,12 @@ static int sun6i_dma_pause(struct dma_chan *chan)
>  	dev_dbg(dmaengine_chan_dev(chan), "vchan %p: pause\n", &vchan->vc);
>
>  	spin_lock_irqsave(&sdev->lock, flags);
> +	vchan->paused = true;
>  	pchan = vchan->phy;
>  	if (pchan) {
>  		writel(DMA_CHAN_PAUSE_PAUSE,
>  		       pchan->base + DMA_CHAN_PAUSE);
> +		readl(pchan->base + DMA_CHAN_PAUSE);

why need read back here?

Frank
>  	} else {
>  		list_del_init(&vchan->node);
>  	}
> @@ -960,12 +967,14 @@ static int sun6i_dma_resume(struct dma_chan *chan)
>  	spin_lock(&vchan->vc.lock);
>  	pchan = vchan->phy;
>
> +	vchan->paused = false;
>  	if (pchan) {
>  		writel(DMA_CHAN_PAUSE_RESUME,
>  		       pchan->base + DMA_CHAN_PAUSE);
> -	} else if (!list_empty(&vchan->vc.desc_issued)) {
> +	} else if (!list_empty(&vchan->vc.desc_issued) && list_empty(&vchan->node)) {
>  		list_add_tail(&vchan->node, &sdev->pending);
>  	}
> +	tasklet_schedule(&sdev->task);
>
>  	spin_unlock(&vchan->vc.lock);
>  	spin_unlock_irqrestore(&sdev->lock, flags);
> @@ -994,6 +1003,7 @@ static int sun6i_dma_terminate_all(struct dma_chan *chan)
>  	}
>
>  	vchan->cyclic = false;
> +	vchan->paused = false;
>  	vchan_get_all_descriptors(&vchan->vc, &head);
>
>  	if (pchan) {
> @@ -1040,6 +1050,8 @@ static enum dma_status sun6i_dma_tx_status(struct dma_chan *chan,
>  	spin_lock_irqsave(&sdev->lock, flags);
>  	spin_lock(&vchan->vc.lock);
>  	ret = dma_cookie_status(chan, cookie, state);
> +	if (ret == DMA_IN_PROGRESS && vchan->paused)
> +		ret = DMA_PAUSED;
>  	if (ret == DMA_COMPLETE || !state)
>  		goto out;
>  	pchan = vchan->phy;
> @@ -1074,7 +1086,7 @@ static void sun6i_dma_issue_pending(struct dma_chan *chan)
>  	spin_lock(&vchan->vc.lock);
>
>  	if (vchan_issue_pending(&vchan->vc)) {
> -		if (!vchan->phy && list_empty(&vchan->node)) {
> +		if (!vchan->paused && !vchan->phy && list_empty(&vchan->node)) {
>  			list_add_tail(&vchan->node, &sdev->pending);
>  			tasklet_schedule(&sdev->task);
>  			dev_dbg(dmaengine_chan_dev(chan), "vchan %p: issued\n",
>
> --
> 2.53.0
>