linux-kernel - Re: [PATCH] pm: sleep: do not set is_prepared when no_pm

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Message-ID: <2d012670.aff7.191b7a2d57c.Coremail.00107082@163.com>
Date: Tue, 3 Sep 2024 19:26:27 +0800 (CST)
From: "David Wang" <00107082@....com>
To: "Greg KH" <gregkh@...uxfoundation.org>
Cc: rafael@...nel.org, pavel@....cz, linux-pm@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] pm: sleep: do not set is_prepared when no_pm_callbacks
 is set

HI, 

At 2024-09-03 18:23:55, "Greg KH" <gregkh@...uxfoundation.org> wrote:
>On Mon, Sep 02, 2024 at 08:59:33PM +0800, David Wang wrote:
>> When resume, a parent device with no pm callbacks
>> would have "is_prepared" and "direct_complete" bit
>> set, and skip the "fib" chance to unset "is_prepared"
>> in device_resume because of the direct_complete bit.
>> This will trigger a kernel warning when resume its child
>> For example, when suspend system with an USB webcam
>> opened, following warning would show up during resume:
>> 
>>  >usb 3-1.1: reset high-speed USB device number 4 using xhci_hcd
>>  >..
>>  >ep_81: PM: parent 3-1.1:1.1 should not be sleeping
>> 
>> The device parenting relationships are:
>> [usb 3-1.1] << [uvcvideo 3-1.1:1.1] << [ep_81].
>> When resume, since the virtual [uvcvideo 3-1.1:1.1] device
>> has no pm callbacks, it would not clear "is_prepared"
>> once set.  Then, when resume [ep_81], pm module would
>> yield a warn seeing [ep_81]'s parent [uvcvideo 3-1.1:1.1]
>> having "is_prepared".
>> 
>> Do not set "is_prepared" for virtual devices having
>> no pm callbacks can clear those kernel warnings.
>> 
>> Signed-off-by: David Wang <00107082@....com>
>> ---
>>  drivers/base/power/main.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>
>What commit id does this fix?

Well, the state management of PM devices is quite complicated to me, lots of commits make small changes 
and  I cannot identify a single commit that solely introduced the kernel warning when suspend an opened USB webcam.

Most obvious commit seems to be 
aa8e54b559479d0cb7eb632ba443b8cacd20cd4b " "PM / sleep: Go direct_complete if driver has no callbacks"
c62ec4610c40bcc44f2d3d5ed1c312737279e2f3 "PM / core: Fix direct_complete handling for devices with no callbacks"

and I will try revert those logic and update later.
  
 
>
>thanks,
>
>greg k-h


David