Issues with boot time KEXT loading

Q:  My KEXT loads when I hot-plug my device, so why won't it load at boot time?

A: A boot time KEXT other than your own may be matching to your device, namely a KEXT with its OSBundleRequired property set. Once a driver has been matched to a device, it will stay loaded until the device is removed or the system is rebooted.

A common example of this is a composite USB device with a vendor-specific driver. The Apple composite class driver will match at boot time. (The composite class driver has to be a boot time KEXT because it is needed to boot from Mass Storage class devices.) As a result, the vendor-specific driver will not load. But, if the device is hot-plugged, all eligible drivers will then compete for the device and the vendor-specific driver will be a better match than the composite class driver.

The solution is to set the OSBundleRequired property in your Info.plist to the same value as that in the competing boot time driver.

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