linux-kernel - Re: Question about suspend/resume clock handling in dwc3-of-simple.c

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Message-ID: <20160912194349.GA14284@roeck-us.net>
Date:   Mon, 12 Sep 2016 12:43:49 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Felipe Balbi <balbi@...nel.org>
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Question about suspend/resume clock handling in dwc3-of-simple.c

Hi Felipe,

On Mon, Sep 12, 2016 at 10:05:00PM +0300, Felipe Balbi wrote:
> 
> Hi Guenter,
> 
> Guenter Roeck <linux@...ck-us.net> writes:
> > Hi folks,
> >
> > In dwc3-of-simple.c:dwc3_of_simple_remove(), I see the following code.
> >
> > 	for (i = 0; i < simple->num_clocks; i++) {
> >                 clk_unprepare(simple->clks[i]);
> > 		clk_put(simple->clks[i]);
> > 	}
> >
> > What I don't understand is why clk_unprepare() is called instead
> > of clk_disable_unprepare(). Someone told me that it was due to
> > dwc3_of_simple_runtime_suspend(), which would call clk_disable().
> 
> good eyes :-) That was fixed though:
> 
> https://marc.info/?l=linux-usb&m=147343692631868&w=2
> 

Great, thanks!

> > Should it be clk_disable_unprepare(), or maybe something like the
> > following
> >
> > 	if (!pm_runtime_status_suspended(dev))
> > 		clk_disable_unprepare();
> > 	else
> > 		clk_unprepare();
> 
> I'm not sure how balanced those calls are, yeah. I don't have HW to test
> PM with. But note that as it is, there is no actual runtime PM support,
> so clk_disable_unprepare() will always be necessary.
> 
> Perhaps we will find further issues when someone tries to use runtime PM
> with dwc3-of-simple. ;-)
> 

We are working on code derived from it, so unless I can convince the author
that he can not just use clk_unprepare() I suspect we'll hit the problem.
If so, I'll let you know.

Thanks!
Guenter