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

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Message-ID: <20170328145908.GT10760@atomide.com>
Date:   Tue, 28 Mar 2017 07:59:08 -0700
From:   Tony Lindgren <tony@...mide.com>
To:     Moreno Bartalucci <moreno.bartalucci@...norama.it>
Cc:     Bin Liu <b-liu@...com>, 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

* Moreno Bartalucci <moreno.bartalucci@...norama.it> [170327 23:12]:
> > Il giorno 27 mar 2017, alle ore 19:15, Bin Liu <b-liu@...com> ha scritto:
> > 
> > […]
> > 
> > The MUSB otg state machine has been changed in many place since the last
> > time I looked at it, and I am not sure how exactly it works now.
> > 
> > If the $subject patch can correctly keep the VBUS on for host-only mode,
> > we can somehow use dr_modei value to distinguish the mode. We don't have
> > to create a new vbus-always-on-in-host-mode flag. VBUS has to be always
> > on in host-only mode anyway, until some error condition happens.
> > 
> 
> During my research, I used this patch to try to print the status of the usb port:
> 
> --- a/drivers/usb/musb/musb_dsps.c	2017-03-13 09:34:31.000000000 +0100
> +++ b/drivers/usb/musb/musb_dsps.c	2017-03-13 09:36:02.000000000 +0100
> @@ -245,6 +245,8 @@ static void otg_timer(unsigned long _mus
>  	dev_dbg(musb->controller, "Poll devctl %02x (%s)\n", devctl,
>  				usb_otg_state_string(musb->xceiv->otg->state));
> 
> +	dev_emerg(musb->controller, "musb->xceiv->otg->state=%s, musb->port_mode=%d\n", usb_otg_state_string(musb->xceiv->otg->state),(int)musb->port_mode);
> +
>  	spin_lock_irqsave(&musb->lock, flags);
>  	switch (musb->xceiv->otg->state) {
>  	case OTG_STATE_A_WAIT_BCON:
> 
> Unless I did something wrong, maybe it’s worth to notice that before the patch that apparently introduced this bug (2f3fd2c5bde1f94513c3dc311ae64494085ec371) I got nothing printed anywhere.
> With that patch applied, instead, I got the line printed in dmesg.
> I might be wrong but my assumption is that without that patch otg_timer was never called.
> If this is true, it would explain why writing 0 on DEVCTL didn’t bother anything: it never happened.

OK yeah that makes sense.

Thanks,

Tony