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

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Date:	Fri, 05 Sep 2014 17:23:49 +0200
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Krzysztof Kozlowski <k.kozlowski@...sung.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Vinod Koul <vinod.koul@...el.com>,
	Michal Simek <michal.simek@...inx.com>,
	Dan Carpenter <dan.carpenter@...cle.com>,
	dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org
CC:	Kyungmin Park <kyungmin.park@...sung.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Subject: Re: [RFC PATCH] dma: pl330: add Power Management support

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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