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

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Message-ID: <20170327165946.GL10760@atomide.com>
Date:   Mon, 27 Mar 2017 09:59:47 -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 09:23]:
> If I understood your patch, however, if the device (anyone, not just my one) takes longer to switch, VBUS is deasserted anyway.

Yeah some of them can take at least 10 seconds even to enumerate.
So probably we need to have to have some longer timeout set for
OTG_STATE_A_WAIT_BCON, like 20 or 30 seconds.

> Although this patch is working for me, personally I would prefer a solution which would not deassert VBUS. At least on a host only port. Honestly I don’t know how a dual role port should work.

It's been really long time since I read the OTG spec. There
may be some diagram showing the required timeouts in the spec
if there is one for VBUS.

Maybe we need some property to specify vbus-always-on-in-host-mode?

Regards,

Tony