linux-kernel - Re: [PATCH RESEND] phy: phy-twl4030-usb: fix denied runtime access

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Date:   Mon, 17 Sep 2018 15:23:45 -0700
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Andreas Kemnade <andreas@...nade.info>
Cc:     kishon@...com, lee.jones@...aro.org, daniel.thompson@...aro.org,
        wsa@...-dreams.de, linux-omap@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Discussions about the Letux Kernel 
        <letux-kernel@...nphoenux.org>
Subject: Re: [PATCH RESEND] phy: phy-twl4030-usb: fix denied runtime access

On Mon, Sep 17, 2018 at 08:56:34PM +0200, Andreas Kemnade wrote:
> Hi Dmitry,
> 
> On Mon, 17 Sep 2018 10:51:31 -0700
> Dmitry Torokhov <dmitry.torokhov@...il.com> wrote:
> 
> > Hi Andreas,
> > 
> > On Mon, Sep 17, 2018 at 07:22:54AM +0200, Andreas Kemnade wrote:
> > > When runtime is not enabled, pm_runtime_get_sync() returns -EACCESS,
> > > the counter will be incremented but the resume callback not called,
> > > so enumeration and charging will not start properly.
> > > To avoid that happen, wait and try again later.
> > > 
> > > Practically this happens when the device is woken up from suspend by
> > > plugging in usb.
> > > 
> > > Signed-off-by: Andreas Kemnade <andreas@...nade.info>
> > > ---
> > >  drivers/phy/ti/phy-twl4030-usb.c | 9 +++++++++
> > >  1 file changed, 9 insertions(+)
> > > 
> > > diff --git a/drivers/phy/ti/phy-twl4030-usb.c b/drivers/phy/ti/phy-twl4030-usb.c
> > > index a44680d64f9b..1f3cf4e48383 100644
> > > --- a/drivers/phy/ti/phy-twl4030-usb.c
> > > +++ b/drivers/phy/ti/phy-twl4030-usb.c
> > > @@ -552,6 +552,15 @@ static irqreturn_t twl4030_usb_irq(int irq, void *_twl)
> > >  
> > >  	status = twl4030_usb_linkstat(twl);
> > >  
> > > +	/* we might get here too early when runtime is not ready yet
> > > +	 * and we will get an EACCESS later, so try again later
> > > +	 */  
> > 
> > How exactly can this happen? What disables (and later re-enables)
> > runtime PM? 
> If the whole resume process is started by plugging in usb, the
> interrupt will be triggered still in the resume process so that 
> runtime resume is not yet possible, pm_runtime_get_sync() returns
> EACCESS

I see. This all seems a bit wonky, to be honest. I would expect that the
driver would have a suspend routine that disables interrupt and also
configure interrupt for wakeup (enable_irq_wake) and kick bus scanning
from there instead of aborting interrupt handler...

> 
> > How can we guarantee that the interrupt will be
> > re-triggered?
> > 
> The interrupt will not be re-triggered but the handler will be
> called at some other places...
> 
> > > +	if (!pm_runtime_enabled(twl->dev)) {
> > > +		cancel_delayed_work(&twl->id_workaround_work);
> > > +		schedule_delayed_work(&twl->id_workaround_work, HZ);
> > > +		return IRQ_HANDLED;
> > > +	}
> > > +
> ... for example by this delayed work which is already there.

If we decide to keep this, it should be mod_delayed_work() I think.

Thanks.

-- 
Dmitry