On Thu, 1 Nov 2012, Jan Beulich wrote:

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Alan Stern [off-list ref] 11/01/12 4:28 PM >>>

On Wed, 31 Oct 2012, Randy Dunlap wrote:

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on x86_64:

drivers/built-in.o: In function `ehci_reset':
host.c:(.text+0x542a7e): undefined reference to `dbgp_reset_prep'
host.c:(.text+0x542b75): undefined reference to `dbgp_external_startup'
drivers/built-in.o: In function `ehci_bus_resume':
host.c:(.text+0x544705): undefined reference to `dbgp_reset_prep'
host.c:(.text+0x544731): undefined reference to `dbgp_external_startup'

We all forgot about the chipidea driver.  It includes code from 

I didn't even know of this.

quoted

ehci-hcd in a rather unorthodox manner (see 
drivers/usb/chipidea/host.c).

Evidently we need to change your new test in
drivers/usb/early/ehci-dbgp.c to:

#if IS_ENABLED(CONFIG_USB_HCD_EHCI) || defined(CONFIG_USB_CHIPIDEA_HOST)

Upcoming changes to ehci-hcd will make this unnecessary in 3.8, but for 
now we need it.

Which tells me that the CONFIG_USB_SUPPORT version would have been
the better one  (and I would favor that over the ugly variant you suggest
above).

I also suggested IS_ENABLED(CONFIG_USB), which is no uglier than what 
you submitted and would also fix this build error.  How about using it 
instead?

Alan Stern