On 10/25/2012 04:23 AM, Sebastian Andrzej Siewior wrote: > On Wed, Oct 24, 2012 at 08:55:27AM -1000, Mitch Bradley wrote: >>>> So by listing "usb-ehci" in its device ID table, a driver would >>>> essentially be saying that it can handle _all_ USB EHCI controllers. >> >> >> Actually, it means that the driver can handle at least USB EHCI >> controllers that are 100% compatible with the EHCI spec (requiring >> nothing extra). The driver might be able to handle almost-compatible >> controllers, possibly with the help of additional properties. >> >> If a DT node lists "usb-ehci" as a "fallback", it's not guaranteed that >> a given version of that driver will work, but it's worth a try in the >> event that no more-specific driver is matched. > > Not sure fallback is a good term here. The of parses the compatible from left > to right. If the device specific entry is not found (in the driver) then end > up with usb-ehci. If we need a quirk later on we add the device specific entry > to the driver (which will match before usb-ehci is found) and we could use > this entry to apply the quirk. That way you can apply quirks without touch the > firmware / device tree. That's the theory on how the compatible values are used, but in practice, each driver is tested against all the values in a node before moving on to the next driver, so the (current kernel's implementation of the) matching order is not what's needed to make that work. -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
