On 26-05-23, 13:54, Ilpo Järvinen wrote:

pl330_pause() does not set anything to indicate paused condition which causes pl330_tx_status() to return DMA_IN_PROGRESS. This breaks 8250 DMA flush after the fix in commit 57e9af7831dc ("serial: 8250_dma: Fix DMA Rx rearm race"). The function comment for pl330_pause() claims pause is supported but resume is not which is enough for 8250 DMA flush to work as long as DMA status reports DMA_PAUSED when appropriate.

Add PAUSED state for descriptor and mark BUSY descriptors with PAUSED in pl330_pause(). Return DMA_PAUSED from pl330_tx_status() when the descriptor is PAUSED.

Have you noticed the comment in the code which reads:

/* * We don't support DMA_RESUME command because of hardware * limitations, so after pausing the channel we cannot restore * it to active state. We have to terminate channel and setup * DMA transfer again. This pause feature was implemented to * allow safely read residue before channel termination. */

So driver just stops when in pause.

Now the commit 57e9af7831dc returns when in progress state, so am not sure how returning Paused would help here?

Reported-by: Richard Tresidder rtresidd@electromag.com.au Tested-by: Richard Tresidder rtresidd@electromag.com.au Fixes: 88987d2c7534 ("dmaengine: pl330: add DMA_PAUSE feature") Cc: stable@vger.kernel.org Link: https://lore.kernel.org/linux-serial/f8a86ecd-64b1-573f-c2fa-59f541083f1a@el... Signed-off-by: Ilpo Järvinen ilpo.jarvinen@linux.intel.com

---

$ diff -u <(git grep -l -e '.device_pause' -e '->device_pause') <(git grep -l DMA_PAUSED)

...tells there might a few other drivers which do not properly return DMA_PAUSED status despite having a pause function.

drivers/dma/pl330.c | 18 ++++++++++++++++-- 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/drivers/dma/pl330.c b/drivers/dma/pl330.c index 0d9257fbdfb0..daad25f2c498 100644 --- a/drivers/dma/pl330.c +++ b/drivers/dma/pl330.c @@ -403,6 +403,12 @@ enum desc_status { * of a channel can be BUSY at any time. */ BUSY,

• /*

• * Pause was called while descriptor was BUSY. Due to hardware
  

• * limitations, only termination is possible for descriptors
  

• * that have been paused.
  

• */
  

• PAUSED, /*
  • Sitting on the channel work_list but xfer done
  • by PL330 core

@@ -2041,7 +2047,7 @@ static inline void fill_queue(struct dma_pl330_chan *pch) list_for_each_entry(desc, &pch->work_list, node) { /* If already submitted */

• if (desc->status == BUSY)
  

• if (desc->status == BUSY || desc->status == PAUSED)
  continue;
  

ret = pl330_submit_req(pch->thread, desc); @@ -2326,6 +2332,7 @@ static int pl330_pause(struct dma_chan *chan) { struct dma_pl330_chan *pch = to_pchan(chan); struct pl330_dmac *pl330 = pch->dmac;

• struct dma_pl330_desc *desc; unsigned long flags;

pm_runtime_get_sync(pl330->ddma.dev); @@ -2335,6 +2342,10 @@ static int pl330_pause(struct dma_chan *chan) _stop(pch->thread); spin_unlock(&pl330->lock);

• list_for_each_entry(desc, &pch->work_list, node) {

• if (desc->status == BUSY)
  

• 	desc->status = PAUSED;
  

• } spin_unlock_irqrestore(&pch->lock, flags); pm_runtime_mark_last_busy(pl330->ddma.dev); pm_runtime_put_autosuspend(pl330->ddma.dev);

@@ -2425,7 +2436,7 @@ pl330_tx_status(struct dma_chan *chan, dma_cookie_t cookie, else if (running && desc == running) transferred = pl330_get_current_xferred_count(pch, desc);

• else if (desc->status == BUSY)
  

• else if (desc->status == BUSY || desc->status == PAUSED)
  /*
   * Busy but not running means either just enqueued,
   * or finished and not yet marked done
  

@@ -2442,6 +2453,9 @@ pl330_tx_status(struct dma_chan *chan, dma_cookie_t cookie, case DONE: ret = DMA_COMPLETE; break;

• 	case PAUSED:
  

• 		ret = DMA_PAUSED;
  

• 		break;
  case PREP:
  case BUSY:
  	ret = DMA_IN_PROGRESS;
  

-- 2.30.2