linux-kernel - Re: usb: dwc3: gadget: Change runtime pm function for DWC3 runtime suspend

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Date:   Tue, 16 Feb 2021 10:30:52 +0900
From:   Jung Daehwan <dh10.jung@...sung.com>
To:     Alan Stern <stern@...land.harvard.edu>,
        Wesley Cheng <wcheng@...eaurora.org>
Cc:     Felipe Balbi <balbi@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "open list:DESIGNWARE USB3 DRD IP DRIVER" <linux-usb@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: usb: dwc3: gadget: Change runtime pm function for DWC3 runtime
 suspend

Hello, Alan

On Mon, Feb 15, 2021 at 12:41:45PM -0500, Alan Stern wrote:
> On Mon, Feb 15, 2021 at 11:38:58AM +0900, Daehwan Jung wrote:
> > It seems pm_runtime_put calls runtime_idle callback not runtime_suspend callback.
> 
> How is this fact related to your patch?

I think we should cause dwc3_runtime_suspend at the time.
That's why I use pm_runtime_put_sync_suspend.

> 
> > It's better to use pm_runtime_put_sync_suspend to allow DWC3 runtime suspend.
> 
> Why do you think it is better?  The advantage of pm_runtime_put is that 
> it allows the suspend to occur at a later time in a workqueue thread, so 
> the caller doesn't have to wait for the device to go into suspend.
> 

We can assume DWC3 was already in suspend state if pm_runtime_get_sync
returns 0. DWC3 resumes due to pm_rumtime_get_sync but it doesn't
re-enter runtime_suspend but runtime_idle. pm_runtime_put decreases
usage_count but doesn't cause runtime_suspend.

1. USB disconnected
2. UDC unbinded
3. DWC3 runtime suspend
4. UDC binded unexpectedly
5. DWC3 runtime resume (pm_runtime_get_sync)
6. DWC3 runtime idle (pm_runtime_put)
   -> DWC3 runtime suspend again (pm_runtime_put_sync_suspend)

I've talked with Wesley in other patch.

usbb: dwc3: gadget: skip pullup and set_speed after suspend
patchwork.kernel.org/project/linux-usb/patch/1611113968-102424-1-git-send-email-dh10.jung@...sung.com

@ Wesley

I think We should guarantee DWC3 enters suspend again at the time.
How do you think?

Best Regards,
Jung Daehwan

> Alan Stern
> 


> > Signed-off-by: Daehwan Jung <dh10.jung@...sung.com>
> > ---
> >  drivers/usb/dwc3/gadget.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
> > index aebcf8e..4a4b93b 100644
> > --- a/drivers/usb/dwc3/gadget.c
> > +++ b/drivers/usb/dwc3/gadget.c
> > @@ -2229,7 +2229,7 @@ static int dwc3_gadget_pullup(struct usb_gadget *g, int is_on)
> >  	 */
> >  	ret = pm_runtime_get_sync(dwc->dev);
> >  	if (!ret || ret < 0) {
> > -		pm_runtime_put(dwc->dev);
> > +		pm_runtime_put_sync_suspend(dwc->dev);
> >  		return 0;
> >  	}
> >  
> > -- 
> > 2.7.4
> > 
>