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

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Date:	Thu, 15 Aug 2013 00:59:29 +0100
From:	Mark Brown <broonie@...nel.org>
To:	Paul Zimmerman <Paul.Zimmerman@...opsys.com>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Rob Herring <rob.herring@...xeda.com>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Stephen Warren <swarren@...dotorg.org>,
	Ian Campbell <ian.campbell@...rix.com>,
	Felipe Balbi <balbi@...com>,
	Grant Likely <grant.likely@...aro.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.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

On Wed, Aug 14, 2013 at 08:16:56PM +0000, Paul Zimmerman wrote:

> Mark's original complaint about USB was this:
> 
> > 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.

> This sounds to me like the normal discovery mechanism for USB isn't getting
> kicked off because no Connect Status Change is being triggered on the root
> port when the hub is brought online using the GPIOs. Maybe the port has
> been runtime suspended because no device was attached originally?

> So maybe the only thing needed for USB is a way to tell the parent port to
> frob its port control bits to try to determine if a device is now present.
> (set Wake on Connect Enable? Do a Port Reset? Cycle the Port Power bit if
> possible?)

No, that's not required in this case - the case is the opposite one to
the one you describe.  Host starting first then hub works fine, if the
host does go into a low power mode it seems to notice the hub appearing
just fine.  Hub then host fails for some reason which I don't know.

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