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

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Message-ID: <20170511193810.GX3489@atomide.com>
Date:   Thu, 11 May 2017 12:38:11 -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> [170511 12:23]:
> On Thu, May 11, 2017 at 02:10:05PM -0500, Bin Liu wrote:
> [...]
> > > > > The otg state machine implementation in the musb drivers are kind of strange.
> > > > > OTG_STATE_A_WAIT_BCON suppose to be a steady state when no usb device is
> > > > > attached, but the musb drivers use it as a transient state to handle error
> > > > > cases, such as overcurrent ot HNP timeout, which is done in the 'case
> > > > > OTG_STATE_A_WAIT_BCON' branch in otg_timer() (or dsps_check_status() for dsps
> > > > > glue).
> > > > > 
> > > > > Then later when 2f3fd2c5bde1 adds
> > > > > 
> > > > > -       /* Poll for ID change in OTG port mode */
> > > > > -       if (musb->xceiv->otg->state == OTG_STATE_B_IDLE &&
> > > > > -                       musb->port_mode == MUSB_PORT_MODE_DUAL_ROLE)
> > > > > +       /* Poll for ID change and connect */
> > > > > +       switch (musb->xceiv->otg->state) {
> > > > > +       case OTG_STATE_B_IDLE:
> > > > > +       case OTG_STATE_A_WAIT_BCON:
> > > > >                 mod_timer(&glue->timer, jiffies +
> > > > >                                 msecs_to_jiffies(wrp->poll_timeout));
> > > > > +               break;
> > > > > 
> > > > > which causes dsps_check_status (or otg_timer()) got called for a normal
> > > > > condition with OTG_STATE_A_WAIT_BCON, then turns off VBUS...
> > > > > 
> > > > > Will try to see how to solve this...
> > > > 
> > > > Maybe we just need to add back the earlier check for non-OTG devices
> > > > "musb->port_mode == MUSB_PORT_MODE_DUAL_ROLE" into case
> > > > OTG_STATE_A_WAIT_BCON?
> > > 
> > > Not sure if it will work. The check is to kick out device-only mode.
> > > DUAL_ROLE means both OTG and host-only.
> > > 
> > > > 
> > > > Not sure if am335x configured with host port ever idle that way,
> > > > but maybe VBUS can be kept on with musb idle.
> > > 
> > > Just tried to remove 
> > > 
> > > +       case OTG_STATE_A_WAIT_BCON:
> > > 
> > > for the polling, but the port stops detecting device attach, musb
> > > power/devctl registers are good, trying to see why... maybe related to
> > > PM state?
> > 
> > usb_otg_hs is idle, so not able to detect attach. So need to get the
> > timer rolling in here to make it detect working.
> > Maybe need to add a flag in dsps_check_status() to not turn off vbus in
> > this case? Really don't like the idea...

Yeah that's what I recall too. The timer is needed until the m3 can
implement an irqchip and we can set that up as the irq for the host
only port.

> I am not sure I gave out the picture clearly.
> 
> Before added the runtime PM support, in host mode (devctl=0x19) the
> otg_timer is stopped, the controller is ready to detect attach.
> 
> Later when added the runtime PM support, usb_otg_hs hwmod becomes idle
> when a device is detached, so the otg_timer is needed to keep hwmod
> enable/idle periodically to detect attach, which triggers the issue
> because otg_timer() turns off vbus unconditionally when otg state is
> OTG_STATE_A_WAIT_BCON.

I wonder if just keeping VBUS on longer in OTG_STATE_A_WAIT_BCON
solves this issue? It seems the issue is with modems that get
reconfigured after the initial enumeration?

We could poll for new devices every 2 seconds, if anything is seen
on the bus, keep VBUS on at least 20 seconds, then if nothing is
found, poll every 2 seconds again.

Regards,

Tony