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

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Message-ID: <20110523083208.GM3095@legolas.emea.dhcp.ti.com>
Date:	Mon, 23 May 2011 11:32:18 +0300
From:	Felipe Balbi <balbi@...com>
To:	Tanya Brokhman <tlinder@...eaurora.org>
Cc:	balbi@...com, greg@...ah.com, linux-usb@...r.kernel.org,
	linux-arm-msm@...r.kernel.org, ablay@...eaurora.org,
	'open list' <linux-kernel@...r.kernel.org>,
	Sarah Sharp <sarah.a.sharp@...ux.intel.com>
Subject: Re: [PATCH v12 7/8] usb: Adding SuperSpeed support to dummy_hcd

hi,

On Mon, May 23, 2011 at 11:18:53AM +0300, Tanya Brokhman wrote:
> > > > > +
> > > > > +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

take a look at xhci-ring.c for an example :-)

see that it check whether the attached device is a USB3.0 device or
USB2.0/1.1 device and chooses hcd or shared_hcd accordingly.

> 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?

nope. If dummy_hcd was a SW xhci implementation then it should be taken
care by upper layers, but since this is a complete SW non-standard Host
interface, then we need to handle the whole thing.

> 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

not the exact wording of the Specs but it should work :-)

> SS cable), should it still enumerate as a HS device? It seems to me that the
> answer is no but I'm not sure...

the USB3 host shouldn't enumerate but it has the shared_hcd which is
USB2.0 compliant.

> > > 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...

Maybe Sarah can give more details on this one. Sarah, what happens if we
attach USB2.0 device to USB3.0 roothub ?

-- 
balbi

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