linux-kernel - Re: Non-enumerable devices on USB and other enumerable buses

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]

Message-ID: <20130812110714.GA6616@e106331-lin.cambridge.arm.com>
Date:	Mon, 12 Aug 2013 12:07:14 +0100
From:	Mark Rutland <mark.rutland@....com>
To:	Mark Brown <broonie@...nel.org>, Olof Johansson <olof@...om.net>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	Pawel Moll <Pawel.Moll@....com>,
	Stephen Warren <swarren@...dotorg.org>,
	Ian Campbell <ian.campbell@...rix.com>,
	Felipe Balbi <balbi@...com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	"devicetree@...nel.org" <devicetree@...nel.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Non-enumerable devices on USB and other enumerable buses

[Adding Olof]

On Mon, Aug 12, 2013 at 10:51:36AM +0100, Mark Brown wrote:
> On Sun, Aug 11, 2013 at 09:53:01PM -0400, Alan Stern wrote:
> > On Sun, 11 Aug 2013, Mark Brown wrote:
> 
> > > One example that's bugging me right now is that on the Insignal Arndale
> > > platform there's a USB hub connected to one of the USB ports on the SoC
> > > (not as a PHY, it seems we also need the internal PHY running to talk to
> > > the device).  The hub needs to be "plugged" into the SoC after the SoC
> > > USB controller has started with some GPIOs so we need to tell the system
> > > that the hub exists and needs to be synchronised with the USB controller.
> 
> > On the surface, this seems like a particularly simple case.  Why wait 
> > until the SoC's USB controller has started?  Why not "plug in" the hub 
> > via the GPIOs right from the beginning?
> 
> I tried that, it doesn't seem to work - for some reason it seems that
> the hub is only successfully enumerated if it starts after its parent is
> running.  I don't know enough about USB to speculate on why that might
> be, the GPIOs are brining the device out of reset not applying power or
> anything.
> 
> > > Another case that's going to be problematic once it's in mainline is
> > > Slimbus - this is a bus used in some embedded audio subsystems which is
> > > enumerable in a similar manner to USB but where the devices on the bus
> > > are normally powered up only on demand (causing them to hotplug when
> > > used and unplug when idle) and have at least interrupt lines wired to
> > > the SoC using a normal interrupt outside the enumerable bus.
> 
> > That is indeed more difficult, because it requires geniune cooperation 
> > between the bus and platform subsystems.
> 
> Yeah.  You might want to do the same with for example a USB network
> controller when you're in flight only mode, that seems to be one of the
> more common reasons for doing this sort of thing with USB.

As I understand it, the wifi chip on the Snow Chromebook has a similar
issue -- it hangs off of a probeable SDIO bus, but needs a regulator
poked for it to turn on and become probeable (see
exynos_wifi_bt_set_power in [1]).

Thanks,
Mark.

[1] http://git.chromium.org/gitweb/?p=chromiumos/third_party/kernel.git;a=blob;f=arch/arm/mach-exynos/mach-exynos5-dt.c;h=d131241ea78b7d89df21e676e284ddfd369b4da0;hb=refs/heads/chromeos-3.4
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/