DEC: Limit PMAX memory probing to R3k systems

stable inclusion
from stable-v5.10.110
commit 785ffce44a1f786392dec7d3555a55275547a7fe
bugzilla: https://gitee.com/openeuler/kernel/issues/I574AL

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=785ffce44a1f786392dec7d3555a55275547a7fe

--------------------------------

commit 244eae91 upstream.

Recent tightening of the opcode table in binutils so as to consistently
disallow the assembly or disassembly of CP0 instructions not supported
by the processor architecture chosen has caused a regression like below:

arch/mips/dec/prom/locore.S: Assembler messages:
arch/mips/dec/prom/locore.S:29: Error: opcode not supported on this processor: r4600 (mips3) `rfe'

in a piece of code used to probe for memory with PMAX DECstation models,
which have non-REX firmware.  Those computers always have an R2000 CPU
and consequently the exception handler used in memory probing uses the
RFE instruction, which those processors use.

While adding 64-bit support this code was correctly excluded for 64-bit
configurations, however it should have also been excluded for irrelevant
32-bit configurations.  Do this now then, and only enable PMAX memory
probing for R3k systems.
Reported-by: NJan-Benedict Glaw <jbglaw@lug-owl.de>
Reported-by: NSudip Mukherjee <sudipm.mukherjee@gmail.com>
Signed-off-by: NMaciej W. Rozycki <macro@orcam.me.uk>
Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org # v2.6.12+
Signed-off-by: NThomas Bogendoerfer <tsbogend@alpha.franken.de>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NYu Liao <liaoyu15@huawei.com>
Reviewed-by: NWei Li <liwei391@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

arch/mips/dec/prom/Makefile

@@ -6,4 +6,4 @@
 
 lib-y			+= init.o memory.o cmdline.o identify.o console.o
 
-lib-$(CONFIG_32BIT)	+= locore.o
+lib-$(CONFIG_CPU_R3000)	+= locore.o

arch/mips/include/asm/dec/prom.h

@@ -43,16 +43,11 @@
  */
 #define REX_PROM_MAGIC		0x30464354
 
-#ifdef CONFIG_64BIT
-
-#define prom_is_rex(magic)	1	/* KN04 and KN05 are REX PROMs.  */
-
-#else /* !CONFIG_64BIT */
-
-#define prom_is_rex(magic)	((magic) == REX_PROM_MAGIC)
-
-#endif /* !CONFIG_64BIT */
-
+/* KN04 and KN05 are REX PROMs, so only do the check for R3k systems.  */
+static inline bool prom_is_rex(u32 magic)
+{
+	return !IS_ENABLED(CONFIG_CPU_R3000) || magic == REX_PROM_MAGIC;
+}
 
 /*
  * 3MIN/MAXINE PROM entry points for DS5000/1xx's, DS5000/xx's and