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

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Date:	Mon, 23 May 2011 11:18:53 +0300
From:	"Tanya Brokhman" <tlinder@...eaurora.org>
To:	<balbi@...com>
Cc:	<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

> > > > +
> > > > +static struct dummy_hcd_module_parameters mod_data = {
> > > > +	.is_super_speed = false
> > > > +};
> > > > +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 :-)

Yes this will be the best solution :) But as I said, the enumeration occurs
not in dummy_hcd thus I'm not sure how dummy_hcd can find out that it failed
in order to reconnect the device to hs_hcd. And I'm not sure that dummy_hcd
should care whether the enumeration succeeds or fails. It seems to me that
this should be handled by upper levels. Shouldn't it?
But we're discussing a more general issue; do you remember what the usb30
spec sais about this? I mean when connecting a HS device to a SS port (over
SS cable), should it still enumerate as a HS device? It seems to me that the
answer is no but I'm not sure...

> 
> > 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 :-)
> 

Hmmm.... I have v2.6.38 installed on my Linux-host at the moment and I just
verified that when connecting a Gadget driver without SS descriptors over SS
connection - the enumeration fails. Was this fixed in v2.6.39? It will take
me some time to upgrade to v2.6.39  and verify but I have to do it any way
so I'll give it a shot...

Best regards,
Tanya Brokhman
Consultant for Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum

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