linux-kernel - Re: [PATCH 1/6] dmaengine: tegra-apb: Correct runtime-pm usage

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Message-ID: <20151029015709.GE18368@vkoul-mobl.iind.intel.com>
Date:	Thu, 29 Oct 2015 10:57:13 +0900
From:	Vinod Koul <vinod.koul@...el.com>
To:	Jon Hunter <jonathanh@...dia.com>
Cc:	Laxman Dewangan <ldewangan@...dia.com>,
	Stephen Warren <swarren@...dotorg.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Alexandre Courbot <gnurou@...il.com>,
	dmaengine@...r.kernel.org, linux-tegra@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/6] dmaengine: tegra-apb: Correct runtime-pm usage

On Wed, Oct 28, 2015 at 01:32:12PM +0000, Jon Hunter wrote:
> 
> On 28/10/15 07:03, Vinod Koul wrote:
> > On Fri, Oct 16, 2015 at 09:25:52AM +0100, Jon Hunter wrote:
> >> @@ -1182,14 +1182,11 @@ static int tegra_dma_alloc_chan_resources(struct dma_chan *dc)
> >>  {
> >>  	struct tegra_dma_channel *tdc = to_tegra_dma_chan(dc);
> >>  	struct tegra_dma *tdma = tdc->tdma;
> >> -	int ret;
> >>  
> >>  	dma_cookie_init(&tdc->dma_chan);
> >>  	tdc->config_init = false;
> >> -	ret = clk_prepare_enable(tdma->dma_clk);
> >> -	if (ret < 0)
> >> -		dev_err(tdc2dev(tdc), "clk_prepare_enable failed: %d\n", ret);
> >> -	return ret;
> >> +
> >> +	return pm_runtime_get_sync(tdma->dev);
> > 
> > Alloc channel is supposed to return number of descriptors allocated and if
> > pm_runtime_get_sync() returns postive values we get wrong return!
> 
> Yes I will fix. I assume that returning 0 is allowed if no descriptors
> are allocated here. So much for correcting rpm usage ;-)

Yes 0 is allowed...

> >>  static int tegra_dma_pm_suspend(struct device *dev)
> >>  {
> >>  	struct tegra_dma *tdma = dev_get_drvdata(dev);
> >> -	int i;
> >> -	int ret;
> >> +	int i, ret;
> >>  
> >>  	/* Enable clock before accessing register */
> >> -	ret = tegra_dma_runtime_resume(dev);
> >> +	ret = pm_runtime_get_sync(dev);
> > 
> > If you are runtime suspended then core will runtime resume you before
> > invoking suspend, so why do we need this
> 
> Is this change now in the mainline? Do you have commit ID for that?
> 
> I recall the last time we discussed this that Rafael said that they were
> going to do that, but he said as a rule of thumb if you need to resume
> it, resume it [0].

IIRC this has been always the behaviour, at least I see this when I test the
devices

-- 
~Vinod
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