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

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Message-ID: <20170512145849.GE3489@atomide.com>
Date:   Fri, 12 May 2017 07:58:49 -0700
From:   Tony Lindgren <tony@...mide.com>
To:     Bin Liu <b-liu@...com>,
        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

* 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.

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.

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: