Re: [RFC PATCH] dma: pl330: add Power Management support

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On 09/05/2014 05:06 PM, Krzysztof Kozlowski wrote:
[...]
@@ -2168,11 +2199,23 @@ static void pl330_issue_pending(struct dma_chan *chan)
  {
  	struct dma_pl330_chan *pch = to_pchan(chan);
  	unsigned long flags;
+	bool power_up;

  	spin_lock_irqsave(&pch->lock, flags);
+	power_up = list_empty(&pch->work_list);
  	list_splice_tail_init(&pch->submitted_list, &pch->work_list);
  	spin_unlock_irqrestore(&pch->lock, flags);

+	if (power_up) {
+		/*
+		 * Warn on nothing pending. This may break our pm_runtime
+		 * usage counter as it is updated on work_list emptiness
+		 * status.
+		 */
+		WARN_ON(list_empty(&pch->work_list));
+		pm_runtime_get_sync(pch->dmac->ddma.dev);

Unfortunately this does not work. pm_runtime_get_sync() may sleep, where as the issue_pending callback needs to be able to run from contexts in which sleeping is not possible.

+	}
+
  	pl330_tasklet((unsigned long)pch);
  }

[...]
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