linux-kernel - Re: [PATCH] net/wireless: enable wiphy device to suspend/resume asynchronously

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Date:	Mon, 24 Aug 2015 09:38:38 +0200
From:	Johannes Berg <johannes@...solutions.net>
To:	"Fu, Zhonghui" <zhonghui.fu@...ux.intel.com>,
	Arend van Spriel <arend@...adcom.com>,
	Emmanuel Grumbach <egrumbach@...il.com>
Cc:	David Miller <davem@...emloft.net>,
	"linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Subject: Re: [PATCH] net/wireless: enable wiphy device to suspend/resume
 asynchronously

On Mon, 2015-08-24 at 11:45 +0800, Fu, Zhonghui wrote:
> 
> On 2015/8/17 16:46, Arend van Spriel wrote:
> > + Rafael
> > 
> > On 08/17/2015 09:29 AM, Johannes Berg wrote:
> > > On Mon, 2015-08-17 at 09:48 +0800, Fu, Zhonghui wrote:
> > > > 
> > > > The suspend/resume timing of wiphy device and related devices 
> > > > will be
> > > > ensured by their parent/child relationship. So, enabling wiphy 
> > > > device
> > > > to suspend/resume asynchronously does not change any 
> > > >  dependency. It
> > > > can only take advantage of multicore and improve system
> > > > suspend/resume speed.
> > > > 
> > > 
> > > You're going to have to explain that to me, because I don't see 
> > > that.
> > > All I see is that when looking at a device, if async is possible, 
> > > it
> > > gets added to an async work, and if async is not possible then it 
> > > gets
> > > done immediately. Even putting aside the question of whether or 
> > > not
> > > async is ordered or not (I don't know), if the wiphy is async and 
> > > the
> > > PCI (or other bus) device isn't, then it seems they could get 
> > > handled
> > > out of order, no? Or is there some magic code somewhere that I'm
> > > missing that explicitly waits for the async of the parent/child
> > > relationship?
> > 
> > This patch got me worried as well. Can't find the magic either. 
> > Maybe Rafael can give some hints here.
> 
> "dpm_wait_for_children" function will be invoked in 
> "__device_suspend", "__device_suspend_late", and 
> "__device_suspend_noirq" functions to synchronize the child 
> relationship. "dpm_wait" function will be invoked in 
> "device_resume_noirq", "device_resume_early", and "device_resume" 
> functions to synchronize the parent relationship. If two devices have 
> parent/child relationship, but different suspend/resume mode(sync or 
> async), this will have no impact to PM timing order between them. 
> Because all devices will use "__device_suspend", 
> "__device_suspend_late" ... functions to complete their PM 
> transition.
> 

Ok, good point. For the unaware here, can you please resend with a
commit message amended with some of this information?

thanks,
johannes
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