MIPS: r4k-bugs64: Limit R4k bug checks to affected systems

Only build the checks for R4k errata workarounds if we expect that the
kernel might actually run on a system with an R4k CPU - ie.
CONFIG_SYS_HAS_CPU_R4X00=y & we're targeting a pre-MIPSr1 ISA revision.

Rename cpu-bugs64.c to r4k-bugs64.c to indicate the fact that the code
is specific to R4k CPUs.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org

arch/mips/Kconfig

@@ -2554,6 +2554,10 @@ config CPU_R4000_WORKAROUNDS
 config CPU_R4400_WORKAROUNDS
 	bool
 
+config CPU_R4X00_BUGS64
+	bool
+	default y if SYS_HAS_CPU_R4X00 && 64BIT && (TARGET_ISA_REV < 1)
+
 config MIPS_ASID_SHIFT
 	int
 	default 6 if CPU_R3000 || CPU_TX39XX

arch/mips/include/asm/bugs.h

@@ -26,9 +26,8 @@ extern void check_bugs64(void);
 
 static inline void check_bugs_early(void)
 {
-#ifdef CONFIG_64BIT
-	check_bugs64_early();
-#endif
+	if (IS_ENABLED(CONFIG_CPU_R4X00_BUGS64))
+		check_bugs64_early();
 }
 
 static inline void check_bugs(void)
@@ -37,19 +36,18 @@ static inline void check_bugs(void)
 
 	cpu_data[cpu].udelay_val = loops_per_jiffy;
 	check_bugs32();
-#ifdef CONFIG_64BIT
-	check_bugs64();
-#endif
+
+	if (IS_ENABLED(CONFIG_CPU_R4X00_BUGS64))
+		check_bugs64();
 }
 
 static inline int r4k_daddiu_bug(void)
 {
-#ifdef CONFIG_64BIT
+	if (!IS_ENABLED(CONFIG_CPU_R4X00_BUGS64))
+		return 0;
+
 	WARN_ON(daddiu_bug < 0);
 	return daddiu_bug != 0;
-#else
-	return 0;
-#endif
 }
 
 #endif /* _ASM_BUGS_H */

arch/mips/kernel/Makefile

@@ -80,7 +80,7 @@ obj-$(CONFIG_KGDB)		+= kgdb.o
 obj-$(CONFIG_PROC_FS)		+= proc.o
 obj-$(CONFIG_MAGIC_SYSRQ)	+= sysrq.o
 
-obj-$(CONFIG_64BIT)		+= cpu-bugs64.o
+obj-$(CONFIG_CPU_R4X00_BUGS64)	+= r4k-bugs64.o
 
 obj-$(CONFIG_I8253)		+= i8253.o
 

arch/mips/kernel/genex.S

@@ -657,7 +657,7 @@ isrdhwr:
 	.set	pop
 	END(handle_ri_rdhwr)
 
-#ifdef CONFIG_64BIT
+#ifdef CONFIG_CPU_R4X00_BUGS64
 /* A temporary overflow handler used by check_daddi(). */
 
 	__INIT