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

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Message-id: <1410163907.4300.5.camel@AMDC1943>
Date:	Mon, 08 Sep 2014 10:11:47 +0200
From:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
To:	Lars-Peter Clausen <lars@...afoo.de>
Cc:	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,
	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 pią, 2014-09-05 at 17:23 +0200, Lars-Peter Clausen wrote:
> 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.

Thank you for pointing this out. It seems I'll have to find another
solution because I really need to runtime suspend this driver...

Best regards,
Krzysztof

> 
> > +	}
> > +
> >   	pl330_tasklet((unsigned long)pch);
> >   }
> >
> [...]

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