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

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Message-ID: <20170512172134.GI3489@atomide.com>
Date:   Fri, 12 May 2017 10:21:35 -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 08:24]:
> On Fri, May 12, 2017 at 07:58:49AM -0700, Tony Lindgren wrote:
> > 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.

Oh I was just thinking what we might want to do in the future if
we want to cut off VBUS when no devices are connected. If we have
a USB modem for example it might first enumerate as some boot device,
then nothing for 20 seconds while it's booting, and then we have a
different device enumerating after the modem has booted. During this
period we want to keep VBUS on and will go through multiple
OTG_STATE_A_WAIT_BCON states. So we can't really control VBUS using
the OTG_STATE_WHATEVER alone.

Regards,

Tony