[PATCH v3] powerpc xmon: use `dcbf` inplace of `dcbi` instruction for 64bit Book3S

[Balamuruhan S]

Data Cache Block Invalidate (dcbi) instruction implemented back in
PowerPC architecture version 2.03. But as per Power Processor Users Manual
it is obsolete and not supported by POWER8/POWER9 core. Attempt to use of
this illegal instruction results in a hypervisor emulation assistance
interrupt. So, ifdef it out the option `i` in xmon for 64bit Book3S.

0:mon> fi
cpu 0x0: Vector: 700 (Program Check) at [c000000003be74a0]
    pc: c000000000102030: cacheflush+0x180/0x1a0
    lr: c000000000101f3c: cacheflush+0x8c/0x1a0
    sp: c000000003be7730
   msr: 8000000000081033
  current = 0xc0000000035e5c00
  paca    = 0xc000000001910000   irqmask: 0x03   irq_happened: 0x01
    pid   = 1025, comm = bash
Linux version 5.6.0-rc5-g5aa19adac (root at ltc-wspoon6) (gcc version 7.4.0
(Ubuntu 7.4.0-1ubuntu1~18.04.1)) #1 SMP Tue Mar 10 04:38:41 CDT 2020
cpu 0x0: Exception 700 (Program Check) in xmon, returning to main loop
[c000000003be7c50] c00000000084abb0 __handle_sysrq+0xf0/0x2a0
[c000000003be7d00] c00000000084b3c0 write_sysrq_trigger+0xb0/0xe0
[c000000003be7d30] c0000000004d1edc proc_reg_write+0x8c/0x130
[c000000003be7d60] c00000000040dc7c __vfs_write+0x3c/0x70
[c000000003be7d80] c000000000410e70 vfs_write+0xd0/0x210
[c000000003be7dd0] c00000000041126c ksys_write+0xdc/0x130
[c000000003be7e20] c00000000000b9d0 system_call+0x5c/0x68
--- Exception: c01 (System Call) at 00007fffa345e420
SP (7ffff0b08ab0) is in userspace

Signed-off-by: Balamuruhan S <bala24 at linux.ibm.com>
---
 arch/powerpc/xmon/xmon.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
changes in v3:
-------------
Fix Christophe's review comments and rebase it on latest mpe's merge
tree,
	* mention the dcbi obsolete statement based on Power processor
	  users manual in commit message.
	* make #ifdef in a more simple way.
changes in v2:
-------------
Fix review comments from Segher and Michael,
        * change incorrect architecture version 2.01 to 2.03 in commit
          message.
        * ifdef it out the option `i` for PPC_BOOK3S_64 instead to drop
	  it and change the commit message accordingly.

diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
index ea303b7e4e29..7b62d5dcc4a1 100644
--- a/arch/powerpc/xmon/xmon.c
+++ b/arch/powerpc/xmon/xmon.c
@@ -1808,7 +1808,7 @@ static void cacheflush(void)
 		catch_memory_errors = 1;
 		sync();
 
-		if (cmd != 'i') {
+		if (cmd != 'i' || IS_ENABLED(CONFIG_PPC_BOOK3S_64)) {
 			for (; nflush > 0; --nflush, adrs += L1_CACHE_BYTES)
 				cflush((void *) adrs);
 		} else {

base-commit: 1ad3b5ebe084246ad593a22707cd91ef6418c31e
-- 
2.24.1