linux-kernel - Re: [PATCH] usb-musb: keep VBUS on when device is disconnected

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Date:   Fri, 12 May 2017 10:21:44 -0500
From:   Bin Liu <b-liu@...com>
To:     Tony Lindgren <tony@...mide.com>
CC:     Moreno Bartalucci <moreno.bartalucci@...norama.it>,
        Lars Melin <larsm17@...il.com>,
        "linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Alessio Igor Bogani <abogani@...nel.org>
Subject: Re: [PATCH] usb-musb: keep VBUS on when device is disconnected

On Fri, May 12, 2017 at 07:58:49AM -0700, Tony Lindgren wrote:
> * Bin Liu <b-liu@...com> [170512 06:43]:
> > On Thu, May 11, 2017 at 02:06:28PM -0700, Tony Lindgren wrote:
> > > 
> > > Well maybe the minimal fix for now is just pretty much back to
> > > square one of this thread. This should keep VBUS always on.
> > > Then we can figure out some logic to cut VBUS later on.
> > > 
> > > And yeah, the state machine is really hard to follow so some kind
> > > of clean up would be nice.
> > 
> > Okay, figured out why clearing session in OTG_STATE_A_WAIT_BCON, it is
> > not for error condition handling (which is done in musb-core), but for
> > going back to b_idle state from a_host for dual-role mode. otg_timer()
> > (now is dsps_check_status()) was only called for otg port originally, so
> > it wasn't an issue, until started calling it for host mode as well when
> > runtime PM was added.
> 
> OK makes sense.
> 
> > > 8< -------------------
> > > --- a/drivers/usb/musb/musb_dsps.c
> > > +++ b/drivers/usb/musb/musb_dsps.c
> > > @@ -245,7 +245,6 @@ static int dsps_check_status(struct musb *musb, void *unused)
> > >  		dsps_mod_timer_optional(glue);
> > >  		break;
> > >  	case OTG_STATE_A_WAIT_BCON:
> > > -		musb_writeb(musb->mregs, MUSB_DEVCTL, 0);
> > >  		skip_session = 1;
> > >  		/* fall */
> > >  
> > 
> > So the above patch breaks otg port when switching from host to device
> > mode. The following change should solve it. But Tony do you see any way
> > to improve it with glue->vbus_irq?
> 
> OK. No better ideas except I think we should probably have a separate
> timer for keeping VBUS on after state changes eventually.

Currently with the patch below, VBUS is constantly on for host-only
mode, and this is what we want. Why we need a separate timer? No one
cuts VBUs now for host-only mode.

> 
> I guess the real test here would be to connect a USB modem that
> changes state to the am335x-evm OTG port and make sure it works
> with commit similar to d680414d0f42 ("ARM: dts: Configure BeagleBone
> peripheral USB VBUS irq"). And also without configuring the vusb_irq.

I will test w/ and w/o vbus_irq on BeagleBone.

Moreno, would you mind to test the patch below with your modem?

Thanks,
-Bin.

> 
> For the patch below, seems like the way to go for the fix assuming
> it fixes the $subject issue:
> 
> Acked-by: Tony Lindgren <tony@...mide.com>
> 
> > 8< --------------------
> > diff --git a/drivers/usb/musb/musb_dsps.c b/drivers/usb/musb/musb_dsps.c
> > index 9c7ee26ef388..465281244596 100644
> > --- a/drivers/usb/musb/musb_dsps.c
> > +++ b/drivers/usb/musb/musb_dsps.c
> > @@ -245,9 +245,14 @@ static int dsps_check_status(struct musb *musb, void *unused)
> >                 dsps_mod_timer_optional(glue);
> >                 break;
> >         case OTG_STATE_A_WAIT_BCON:
> > +               /* keep VBUS on for host-only mode */
> > +               if (musb->port_mode == MUSB_PORT_MODE_HOST) {
> > +                       dsps_mod_timer_optional(glue);
> > +                       break;
> > +               }
> >                 musb_writeb(musb->mregs, MUSB_DEVCTL, 0);
> >                 skip_session = 1;
> > -               /* fall */
> > +               /* fall through */
> >  
> >         case OTG_STATE_A_IDLE:
> >         case OTG_STATE_B_IDLE: