dmaengine: pl330: Return DMA_PAUSED when transaction is paused

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.

Reported-by: Richard Tresidder <[e-mail]>
Tested-by: Richard Tresidder <[e-mail]>
Fixes: 88987d2c7534 ("dmaengine: pl330: add DMA_PAUSE feature")
Cc: [e-mail]
Link: https://lore.kernel.org/linux-serial/[e-mail]/
Signed-off-by: Ilpo Järvinen <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Vinod Koul <[e-mail]>

drivers/dma/pl330.c

···
 	 */
 	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
 	 */
···
 	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);
···
 {
 	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);
···
 	_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);
···
 		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
···
 			switch (desc->status) {
 			case DONE:
 				ret = DMA_COMPLETE;
+				break;
+			case PAUSED:
+				ret = DMA_PAUSED;
 				break;
 			case PREP:
 			case BUSY: