linux-kernel - Re: [PATCH v3 01/11] usb: phy: Add APIs for runtime power management

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Date:	Thu, 4 Apr 2013 14:26:51 +0530
From:	Vivek Gautam <gautamvivek1987@...il.com>
To:	balbi@...com
Cc:	Alan Stern <stern@...land.harvard.edu>,
	Kishon Vijay Abraham I <kishon@...com>,
	Vivek Gautam <gautam.vivek@...sung.com>,
	linux-usb@...r.kernel.org, linux-samsung-soc@...r.kernel.org,
	linux-omap@...r.kernel.org, linux-kernel@...r.kernel.org,
	gregkh@...uxfoundation.org, sarah.a.sharp@...ux.intel.com,
	rob.herring@...xeda.com, kgene.kim@...sung.com,
	dianders@...omium.org, t.figa@...sung.com, p.paneri@...sung.com
Subject: Re: [PATCH v3 01/11] usb: phy: Add APIs for runtime power management

Hi,


On Thu, Apr 4, 2013 at 12:48 PM, Felipe Balbi <balbi@...com> wrote:
> Hi,
>
> On Wed, Apr 03, 2013 at 02:14:02PM -0400, Alan Stern wrote:
>> > > Lets suppose DWC3 enables runtime_pm on USB 2 type phy,
>> > > it will try to go into suspend state and thereby call runtime_suspend(), if any.
>> > > And PHY will come to active state only when its consumer wakes it up,
>> > > and this consumer is operational
>> > > only when its related PHY is in fully functional state.
>> > > So do we have a situation in which this PHY goes into low power state
>> > > in its runtime_suspend(),
>> > > resulting in non-detection of devices on further attach (since PHY is
>> > > in low power state) ?
>> > >
>> > > Will the controller (like EHCI/OHCI) be functional now ?
>> >
>> > ehci/ohci need to cope with that by calling usb_phy_autopm_get_sync(),
>> > right ? (so does DWC3 :-)
>>
>> Maybe you guys have already got this all figured out -- if so, feel
>> free to ignore this email.
>>
>> Some subsystems handle this issue by calling pm_runtime_get_sync()
>> before probing a driver and pm_runtime_put_sync() after unbinding the
>> driver.  If the driver is runtime-PM-enabled, it then does its own
>> put_sync near the end of its probe routine and get_sync in its release
>> routine.
>
> sounds a bit 'fishy' to me... So a separate entity would call
> pm_runtime_get_sync(), even when we don't have registered dev_pm_ops,
> then drivers need to check if runtime_pm is enabled and call
> pm_runtime_put*() conditionally before returning from probe(). One
> remove, we might have another issue: device is already runtime_suspended
> (due to e.g. autosuspend) when module is removed, a call to
> pm_runtime_put_sync() will be unbalanced. No ?

May be i am misinterpreting !!
If PHYs are runtime-PM enabled (PHY probe calls *runtime_enable*),
then the consumers
need to call pm_runtime_get_sync whever they want to access PHY.
Besides PHYs also need to *put_sync* just before their probe is
finishing, so that it's
availbale for autosuspend.

I, however didn't understand the need of PHY to *get_sync* itself in
release routine.



-- 
Thanks & Regards
Vivek
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