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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Mon, 27 Mar 2017 08:17:01 -0500
From:   Bin Liu <b-liu@...com>
To:     Moreno Bartalucci <moreno.bartalucci@...norama.it>
CC:     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

On Mon, Mar 27, 2017 at 02:53:27PM +0200, Moreno Bartalucci wrote:
> > Il giorno 25 mar 2017, alle ore 08:21, Lars Melin <larsm17@...il.com> ha scritto:
> > 
> >> 
> >> The usb device has been disconnected, why it still cares about VBUS
> >> power?
> > 
> > Morphing devices (3G dongles, wifi dongles, some printers) boots up in install mode, usually only as a virtual cd-rom containing Windows drivers and software.
> > [...]
> > why a host only configured port should cut the VBUS supply, it could be always on right?
> > 
> 
> Yes, that’s exactly the problem I tried to solve with this patch.

Yeah, the problem is clear to me now.

> I have to add that the problem was not there with kernels up to
> 4.8.17, I started to see it with 4.9 and up.
> 
> By git-bisecting kernel sources, it appears this behaviour has been
> introduced by this commit:
> 
> 2f3fd2c5bde1f94513c3dc311ae64494085ec371

It seems this patch changes how OTG_STATE_A_WAIT_VRISE and
OTG_STATE_A_WAIT_BCON are used.
> 
> I also agree that, in my opinion, a host only port should never remove
> the VBUS supply, as it happens on all the PCs (linux+windows+mac) that
> I tested until now.

True. It is just that the musb driver handles both dual-role and
host-only mode.

> 
> I saw this problem on a beaglebone black. Of course I’m available to
> do all the tests that you might suggest me to help you better
> understand the issue.

Thanks for the offer. Please let me look at the problem first, I have a
modem to test.
It is not clear why the original driver clears VBUS in this place, so I
have to ensure your patch is the correct change.

Regards,
-Bin.