Hi, I tried compile 2.2.21rc3 with ISDN on ppc machine and i had that 
messages:

In file included from 
/home/users/dzimi/rpm/BUILD/linux/include/linux/interrupt.h:52,
                 from hysdn_defs.h:19,
                 from hysdn_sched.c:20:
/home/users/dzimi/rpm/BUILD/linux/include/asm/hardirq.h:4: `NR_CPUS' 
undeclared
here (not in a function)
In file included from 
/home/users/dzimi/rpm/BUILD/linux/include/linux/interrupt.h:53,
                 from hysdn_defs.h:19,
                 from hysdn_sched.c:20:
/home/users/dzimi/rpm/BUILD/linux/include/asm/softirq.h:7: `NR_CPUS' 
undeclared
here (not in a function)
/home/users/dzimi/rpm/BUILD/linux/include/asm/softirq.h: In function 
`start_bh_atomic':
/home/users/dzimi/rpm/BUILD/linux/include/asm/softirq.h:77: warning: 
implicit declaration of function `smp_processor_id'
make[3]: *** [hysdn_sched.o] Error 1

Alan, my patch fix it.

>>-- cut here <<--

--- linux.orig/include/asm-ppc/atomic.h Sun Mar 25 18:31:08 2001
+++ linux/include/asm-ppc/atomic.h      Sun Apr  7 20:38:11 2002
@@ -6,6 +6,9 @@
 #define _ASM_PPC_ATOMIC_H_

 #ifdef __SMP__
+
+#include <asm/smp.h>
+
 typedef struct { volatile int counter; } atomic_t;
 #else
 typedef struct { int counter; } atomic_t;
diff -urN linux.orig/include/asm-ppc/hardirq.h 
linux/include/asm-ppc/hardirq.h
--- linux.orig/include/asm-ppc/hardirq.h        Sun Mar 25 18:31:09 2001
+++ linux/include/asm-ppc/hardirq.h     Sun Apr  7 20:38:49 2002
@@ -1,6 +1,8 @@
 #ifndef __ASM_HARDIRQ_H
 #define __ASM_HARDIRQ_H

+#include <linux/tasks.h>
+
 extern unsigned int ppc_local_irq_count[NR_CPUS];

 /*
>>---------<<


Krzysiek Taraszka