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

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Date:	Mon, 24 Aug 2015 11:45:56 +0800
From:	"Fu, Zhonghui" <zhonghui.fu@...ux.intel.com>
To:	Arend van Spriel <arend@...adcom.com>,
	Johannes Berg <johannes@...solutions.net>,
	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 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.


Thanks,
Zhonghui 
>
> Regards,
> Arend
>
>> johannes
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