linux-kernel - Re: [PATCH v12 7/8] usb: Adding SuperSpeed support to dummy

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Date:	Mon, 23 May 2011 10:20:49 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Felipe Balbi <balbi@...com>
cc:	Tanya Brokhman <tlinder@...eaurora.org>, <greg@...ah.com>,
	<linux-usb@...r.kernel.org>, <linux-arm-msm@...r.kernel.org>,
	<ablay@...eaurora.org>, 'open list' <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v12 7/8] usb: Adding SuperSpeed support to dummy_hcd

On Mon, 23 May 2011, Felipe Balbi wrote:

> > > > +module_param_named(is_super_speed, mod_data.is_super_speed, bool,
> > > > +S_IRUGO); MODULE_PARM_DESC(is_super_speed, "true to simulate
> > > > +SuperSpeed connection");
> > > 
> > > you shouldn't need this. You should always enable SuperSpeed for this
> > > driver.
> > 
> > You mean I don't need the module parameter? IMO it's the best way to enable
> > HS connection. If driver->speed=USB_SPEED_SUPER than dummy_hcd will try to
> > enumerate the device on the SS root hub and if the gadget didn't provide SS
> > descriptors - it will fail. Just as it happened before. Finding out from
> 
> then it should hand the device over to the hs_hcd ;-) Meaning it would
> disconnect the device, switch to hs_hcd and reconnect :-)

No.  That doesn't happen with real devices, so there's no reason 
dummy-hcd should do it.

> > dummy_hcd that the enumeration failed is very complicated (if even possible)
> > and I'm not sure that is the right thing to do... If you connect a real
> > device over SS port to xHCI and the device doesn't provide SS descriptors -
> > the enumeration fails and it's ok. But if you connect the same device to a
> > HS port - it should work properly. This is what I tried to simulate with
> > this parameter.
> 
> it doesn't just fails, it gives the device over to the shared_hcd :-)

It does not.  xhci-hcd does not keep track of whether or not 
enumeration succeeds, and it doesn't do anything special when 
enumeration fails.

Alan Stern

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