linux-kernel - Re: [PATCH v2 06/10] usb: xhci: Enable runtime pm in xhci-plat

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Date:	Mon, 4 Mar 2013 10:29:33 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Vivek Gautam <gautamvivek1987@...il.com>
cc:	Vivek Gautam <gautam.vivek@...sung.com>,
	<linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-omap@...r.kernel.org>, <linux-samsung-soc@...r.kernel.org>,
	<gregkh@...uxfoundation.org>, <balbi@...com>,
	<sarah.a.sharp@...ux.intel.com>, <kgene.kim@...sung.com>,
	<kishon@...com>, Doug Anderson <dianders@...omium.org>
Subject: Re: [PATCH v2 06/10] usb: xhci: Enable runtime pm in xhci-plat

On Mon, 4 Mar 2013, Vivek Gautam wrote:

> >> @@ -149,6 +150,8 @@ static int xhci_plat_probe(struct platform_device *pdev)
> >>       if (ret)
> >>               goto put_usb3_hcd;
> >>
> >> +     pm_runtime_enable(&pdev->dev);
> >
> > This is generally not a good idea.  You shouldn't enable a device for
> > runtime PM without first telling the PM core what state it is in.
> >
> Right, but i am not completely sure on any fixed path to follow for
> enabling runtime
> power management on a device. :-(
> Does it become necessary to "pm_runtime_set_active" or
> "pm_runtime_set_suspended" a device
> before "pm_runtime_enable" ?

Yes, it usually is necesary.  And especially here, because the runtime
PM core sets the initial status of every device to RPM_SUSPENDED.

>  pm_runtime_enable would just try to
> decrement the disable_depth
> of the device.

That's right.  And once that happens, the PM core would think the 
device was suspended even though it was really at full power.

Alan Stern

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