patch-2.6.21-rt8 works for ppc arch?

[Ryan]

Hi,

I'm trying to build a 2.6.21 kernel (ppc arch for a 74xx processor)
with the PREEMPT_RT patch "patch-2.6.21-rt8". But I'm having some
compilation errors in the very early stage. The errors are shown
below.

arch/ppc/kernel/asm-offsets.c: In function 'main':
arch/ppc/kernel/asm-offsets.c:148: error: 'struct vdso_data' has no
member named 'tb_orig_stamp'
arch/ppc/kernel/asm-offsets.c:149: error: 'struct vdso_data' has no
member named 'tb_ticks_per_sec'
arch/ppc/kernel/asm-offsets.c:150: error: 'struct vdso_data' has no
member named 'tb_to_xs'
arch/ppc/kernel/asm-offsets.c:151: error: 'struct vdso_data' has no
member named 'stamp_xsec'
arch/ppc/kernel/asm-offsets.c:152: error: 'struct vdso_data' has no
member named 'tb_update_count'
arch/ppc/kernel/asm-offsets.c:153: error: 'struct vdso_data' has no
member named 'tz_minuteswest'
arch/ppc/kernel/asm-offsets.c:154: error: 'struct vdso_data' has no
member named 'tz_dsttime'
arch/ppc/kernel/asm-offsets.c:156: error: 'struct vdso_data' has no
member named 'wtom_clock_sec'
arch/ppc/kernel/asm-offsets.c:157: error: 'struct vdso_data' has no
member named 'wtom_clock_nsec'
make[1]: *** [arch/ppc/kernel/asm-offsets.s] Error 1

I did dig a little deep to find why this error occurred. It turned out
these members are explicitly removed by patch-2.6.21-rt8. See below
exerted from this patch file. It makes me wondering if the PREEMPT_RT
patch ever worked for ppc arch.

Index: linux/include/asm-powerpc/vdso_datapage.h
===================================================================
--- linux.orig/include/asm-powerpc/vdso_datapage.h
+++ linux/include/asm-powerpc/vdso_datapage.h
@@ -74,11 +74,6 @@ struct vdso_data {
 	__u32 icache_size;		/* L1 i-cache size		0x68 */
 	__u32 icache_line_size;		/* L1 i-cache line size		0x6C */

-	/* those additional ones don't have to be located anywhere
-	 * special as they were not part of the original systemcfg
-	 */
-	__s32 wtom_clock_sec;			/* Wall to monotonic clock */
-	__s32 wtom_clock_nsec;
    	__u32 syscall_map_64[SYSCALL_MAP_SIZE]; /* map of syscalls  */
    	__u32 syscall_map_32[SYSCALL_MAP_SIZE]; /* map of syscalls */
 };
@@ -89,15 +84,6 @@ struct vdso_data {
  * And here is the simpler 32 bits version
  */
 struct vdso_data {
-	__u64 tb_orig_stamp;		/* Timebase at boot		0x30 */
-	__u64 tb_ticks_per_sec;		/* Timebase tics / sec		0x38 */
-	__u64 tb_to_xs;			/* Inverse of TB to 2^20	0x40 */
-	__u64 stamp_xsec;		/*				0x48 */
-	__u32 tb_update_count;		/* Timebase atomicity ctr	0x50 */
-	__u32 tz_minuteswest;		/* Minutes west of Greenwich	0x58 */
-	__u32 tz_dsttime;		/* Type of dst correction	0x5C */
-	__s32 wtom_clock_sec;			/* Wall to monotonic clock */
-	__s32 wtom_clock_nsec;
    	__u32 syscall_map_32[SYSCALL_MAP_SIZE]; /* map of syscalls */
 };

The kernel build also had some compilation warnings as follows.

  CC      arch/ppc/kernel/asm-offsets.s
In file included from arch/ppc/include/asm/hw_irq.h:110,
                 from include/asm/system.h:10,
                 from include/linux/list.h:9,
                 from include/linux/signal.h:8,
                 from arch/ppc/kernel/asm-offsets.c:11:
include/linux/irqflags.h:92:1: warning: "raw_local_irq_save" redefined
In file included from include/asm/system.h:10,
                 from include/linux/list.h:9,
                 from include/linux/signal.h:8,
                 from arch/ppc/kernel/asm-offsets.c:11:
arch/ppc/include/asm/hw_irq.h:103:1: warning: this is the location of
the previous definition
In file included from arch/ppc/include/asm/hw_irq.h:110,
                 from include/asm/system.h:10,
                 from include/linux/list.h:9,
                 from include/linux/signal.h:8,
                 from arch/ppc/kernel/asm-offsets.c:11:
include/linux/irqflags.h:97:1: warning: "raw_local_irq_restore" redefined
In file included from include/asm/system.h:10,
                 from include/linux/list.h:9,
                 from include/linux/signal.h:8,
                 from arch/ppc/kernel/asm-offsets.c:11:
arch/ppc/include/asm/hw_irq.h:62:1: warning: this is the location of
the previous definition
In file included from include/linux/time.h:7,
                 from include/linux/timex.h:57,
                 from include/linux/sched.h:51,
                 from arch/ppc/kernel/asm-offsets.c:12:
include/linux/seqlock.h: In function '__read_seqretry':
include/linux/seqlock.h:139: warning: implicit declaration of function
'local_irq_save'
include/linux/seqlock.h:140: warning: implicit declaration of function
'local_irq_restore'

All the failure makes me doubt the correctness of the PREEMPT_RT patch
in 2.6.21 for ppc arch. Has anyone made a RT patch work for ppc arch
in 2.6.21? In other words, is 2.6.21 a good candidate to test a
PREEMPT_RT patch for ppc arch? I understand that ppc arch will
eventually replaced by powerpc arch. Is there active work going on in
ppc arch to support the PREEMPT_RT?

Thanks a lot in advance for your help.
-Ryan.