(PReP 7248) battable address to align

I've got IBM PReP machine, 43P/133 Model 7248 last year,
and was playing with various release of NetBSD, mainly
with netbooting. The summary is listed on
  http://www.ki.nu/hardware/prep/index.html

I think we have some problems.

1. battable address not aligned to proper address
  (or strangely requires some alignment).
  -- this problem are sometimes hidden, happened to
  be aligned --

2. kernel is too large to boot.
  (But my trial using small kernel for mkbootimage
   does not affect the real kernel in effect, sorry
   not knowning the mechanism to boot.

3. Interrupt handling of siop and serial console is not
   properly done at the early stage of boot (if com0 is
   selected for boot console).

The first problem depends on the kernel compiled:
The typical symptom is
  'cursor is just blinking WITH blackout screen'
  
Or hung just after init is started, for example, after following print.
   -----
   boot-device: sd0
   root on sd0a dumps sd0b
   root file system type: ffs

And I believe
  This existed at least in May, 2013. I have not been playing
with the machine almost for a year,
but it seems the problem still exists.

kiyohara@ investigated and this relates to the address of battable.
To know the battable address, you may issue

  modena@makoto 12:23:04/130908(/export/src-current)% \
  src/obj/tooldir.NetBSD-6.1-amd64/bin/powerpc--netbsd-nm \
  src/sys/arch/prep/compile/obj/GENERIC/netbsd | \
  grep ' B ' | sort | grep -3 battable

   00589570 B null_vnodeop_p
   00589588 B prep_clock_mk48txx
   0058958c B iosrtable
   005895cc B battable
   0058a5cc B msgbuf_paddr
   0058a5d0 B openpic_base
   0058a7ec B pckbc_console_attached

  If the last part of address bits are not x000, I don't
believe the kernel to work.  Above are bad (not to work) example.
Attached patch will set battable address to xxx0 0000.

My obserbation may be totally wrong, I'm far to be an expert.
Please correct if wrong.
Thanks a lot,

Index: sys/arch/powerpc/oea/oea_machdep.c
===================================================================
RCS file: /cvs/cvsroot/src/sys/arch/powerpc/oea/oea_machdep.c,v
retrieving revision 1.71
diff -u -u -r1.71 oea_machdep.c
--- sys/arch/powerpc/oea/oea_machdep.c	24 Mar 2014 19:29:59 -0000	1.71
+++ sys/arch/powerpc/oea/oea_machdep.c	5 Jul 2014 06:18:24 -0000
@@ -96,6 +96,10 @@
  */
 static void trap0(void *);
 
+/* to align struct battable in 0 0000, suggested by kiyohara@ */
+__asm (	" .section .bss\n"
+	" .align 5\n");
+
 /* XXXSL: The battable is not initialized to non-zero for PPC_OEA64 and PPC_OEA64_BRIDGE */
 struct bat battable[BAT_VA2IDX(0xffffffff)+1];
 

# I guess for this requirement comes from powerpc/trap_subr.S,
# which truncate lower 3 bits.

modena@makoto 15:48:43/140705(..src-current/src)% cvs annotate sys/arch/powerpc/oea/genassym.cf | grep -3 BAT_ADDR_SHIFT

Annotations for sys/arch/powerpc/oea/genassym.cf
***************
1.23         (matt     18-Jun-11): define       OEACPU_HIGHSPRG OEACPU_HIGHSPRG
1.23         (matt     18-Jun-11): define       OEACPU_ALTIVEC  OEACPU_ALTIVEC
1.1          (matt     03-Feb-03): 
1.26         (matt     01-Feb-12): define       BAT_ADDR_SHIFT  ilog2(BAT_IDX2VA(1))
1.26         (matt     01-Feb-12): 
1.25         (matt     20-Jun-11): define       PTE_REF         PTE_REF
1.25         (matt     20-Jun-11): define       PTE_CHG         PTE_CHG
modena@makoto 15:49:10/140705(..src-current/src)% cvs annotate sys/arch/powerpc/powerpc/trap_subr.S  | grep -3 BAT_ADDR_SHIFT

Annotations for sys/arch/powerpc/powerpc/trap_subr.S
***************
1.42         (matt     31-Jul-03):      mtsprg2 %r30                    /* in SPRG2 */
1.69         (matt     05-Jun-11):      bt      MSR_PR,1f               /* branch if PSL_PR is set */
1.42         (matt     31-Jul-03):      mfdar   %r31                    /* get fault address */
1.73         (matt     01-Feb-12):      rlwinm  %r31,%r31,3+(32-BAT_ADDR_SHIFT),BAT_ADDR_SHIFT-3,28
1.73         (matt     01-Feb-12):                                      /* get segment * 8 */
1.1          (thorpej  16-Nov-00): 
1.1          (thorpej  16-Nov-00):      /* get batu */
modena@makoto 15:49:38/140705(..src-current/src)%

---
Makoto Fujiwara, 
Chiba, Japan, Narita Airport and Disneyland prefecture.