I was trying to determine the operating frequency of the Teensy 4 QSPI flash.
Looking at the code I've found the following.
https://github.com/PaulStoffregen/cores/blob/02944ba831f2804bdffa345dfa86a63ec652f4f9/teensy4/bootdata.c#L60C2-L60C12
deviceType - 1 - Serial Nor
sflashPadType - 4 - Quad...