linux-kernel - Re: [PATCH V2 08/20] dmaengine/amba-pl08x: support runtime PM

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Date:	Thu, 4 Aug 2011 12:01:19 +0530
From:	viresh kumar <viresh.kumar@...com>
To:	"Koul, Vinod" <vinod.koul@...el.com>
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Pratyush ANAND <pratyush.anand@...com>,
	Rajeev KUMAR <rajeev-dlh.kumar@...com>,
	Armando VISCONTI <armando.visconti@...com>,
	Bhupesh SHARMA <bhupesh.sharma@...com>,
	"linus.walleij@...aro.org" <linus.walleij@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Vipin KUMAR <vipin.kumar@...com>,
	Shiraz HASHIM <shiraz.hashim@...com>,
	Amit VIRDI <Amit.VIRDI@...com>,
	Vipul Kumar SAMAR <vipulkumar.samar@...com>,
	"viresh.linux@...il.com" <viresh.linux@...il.com>,
	Deepak SIKRI <deepak.sikri@...com>,
	"dan.j.williams@...el.com" <dan.j.williams@...el.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH V2 08/20] dmaengine/amba-pl08x: support runtime PM

On 08/04/2011 11:06 AM, Koul, Vinod wrote:
> On Thu, 2011-08-04 at 10:49 +0530, viresh kumar wrote:
>> On 08/03/2011 06:09 PM, Russell King - ARM Linux wrote:
>>> On Mon, Aug 01, 2011 at 03:07:18PM +0530, Viresh Kumar wrote:
>> @@ -405,6 +406,7 @@ pl08x_get_phy_channel(struct pl08x_driver_data *pl08x,
>>  		return NULL;
>>  	}
>>  
>> +	pm_runtime_get_sync(&pl08x->adev->dev);
> this should be ideally one of the first things you would do not last.
> get_sync will ensure your .runtime_resume callback is called before it
> returns (if its suspended)
>>  	return ch;
>>  }

Until this point we are not touching the registers at all. And they will
accessed after this point only.

>> +	pm_runtime_put(&adev->dev);
> _put is probe looks suspect, why do you need this here 

To save power.

> as you are already setting the status as active, this _put will decrement your
> usage count and possibly call your runtime_suspend

We set status as active, as amba/bus layer has enabled it before calling
probe and it doesn't put it.

As DMA will not be used until get_phy_channel() is called, so we can save
some energy here too. So i put it here.

-- 
viresh
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