Gayle also has some registers for PCMCIA stuff and Interrupts. If you are already in the linux source take a look into /source/include/asm-m68k/amigayle.h. You should also look into AmigaOS' card.resource autodocs and /resource/card.h.
I guess, exec looks for a Gayle in those registers and if it doesn't find one scsi.device doesn't even start.
My findings on Gayle's registers so far are:
Code:
0xda0000 // Data
0xda0006 // Error | Feature
0xda000a // Sector Count
0xda000e // Sector Number
0xda0012 // Cylinder Low
0xda0016 // Cylinder High
0xda001a // Device / Head
0xda001e // Status | Command
0xda101a // Control
0xda8000 // Gayle Status
0xda9000 // Gayle INTREQ
0xdaa000 // Gayle INTENA
0xdab000 // Gayle Config