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SubjectRE: [PATCH v12 7/8] usb: Adding SuperSpeed support to dummy_hcd
On Wed, 25 May 2011, Tanya Brokhman wrote:

> Ok so just to make sure I understand you correctly:
> You want me to remove the modification made to usb_composite_probe() and
> instead add:
> static struct usb_gadget_driver composite_driver = {
> + .speed = USB_SPEE_SUPER,
> +#else
> .speed = USB_SPEED_HIGH,
> +#endif
> .unbind = composite_unbind,
> And then you'll be ok with change? Or is there anything else?
> If this is it then I'm relieved :) and of course will update the code.

I have looked this over more carefully. It turns out that both of you
have misunderstood the purpose of CONFIG_USB_GADGET_DUALSPEED (and by
extension, CONFIG_USB_GADGET_SUPERSPEED). In fact, the existing
Kconfig file is also wrong.

The _only_ reason for CONFIG_USB_GADGET_DUALSPEED is so that gadget
drivers can use conditional compilation to avoid including the
high-speed descriptors when the UDC doesn't support high-speed
operation. That's all. This means that the
CONFIG_USB_GAGDET_DUALSPEED option does not need to be
user-controllable in Kconfig. It should default to N, and UDC drivers
that support high speed should select it.

The same should be true of CONFIG_USB_GADGET_HIGHSPEED. It should not
be user-controllable. It should default to N, and UDC drivers that
support SuperSpeed operation (after these patches, only dummy-hcd)
should select it.

There remains the other question, about whether composite_driver.speed
should be set to USB_SPEED_SUPER. I think the matter can be settled at
runtime. Iterate through all the function drivers; if all of them
support SuperSpeed and CONFIG_USB_GADGET_SUPERSPEED is enabled then set
composite_driver.speed to USB_SPEED_SUPER. Otherwise, if all of them
support high speed and CONFIG_USB_GADGET_DUALSPEED is enabled then set
composite_driver.speed to USB_SPEED_HIGH. Otherwise set it to

Alan Stern

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