MIPS: Malta: Fix crash in SMP kernel on non-CMP systems.

Since 6be63bbb (lmo) rsp.
af3a1f6f (kernel.org) the Malta code does
no longer probe for presence of GCMP if CMP is not configured.  This means
that the variable gcmp_present well be left at its default value of -1
which normally is meant to indicate that GCMP has not yet been mmapped.
This non-zero value is now interpreted as GCMP being present resulting
in a write attempt to a GCMP register resulting in a crash.

Reported and a build fix on top of my fix by Rob Landley <rob@landley.net>.
Reported-by: Rob Landley <rob@landley.net>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Patchwork: https://patchwork.linux-mips.org/patch/2413/

arch/mips/include/asm/smp-ops.h

@@ -56,8 +56,43 @@ static inline void register_smp_ops(struct plat_smp_ops *ops)
 
 #endif /* !CONFIG_SMP */
 
-extern struct plat_smp_ops up_smp_ops;
-extern struct plat_smp_ops cmp_smp_ops;
-extern struct plat_smp_ops vsmp_smp_ops;
+static inline int register_up_smp_ops(void)
+{
+#ifdef CONFIG_SMP_UP
+	extern struct plat_smp_ops up_smp_ops;
+
+	register_smp_ops(&up_smp_ops);
+
+	return 0;
+#else
+	return -ENODEV;
+#endif
+}
+
+static inline int register_cmp_smp_ops(void)
+{
+#ifdef CONFIG_MIPS_CMP
+	extern struct plat_smp_ops cmp_smp_ops;
+
+	register_smp_ops(&cmp_smp_ops);
+
+	return 0;
+#else
+	return -ENODEV;
+#endif
+}
+
+static inline int register_vsmp_smp_ops(void)
+{
+#ifdef CONFIG_MIPS_MT_SMP
+	extern struct plat_smp_ops vsmp_smp_ops;
+
+	register_smp_ops(&vsmp_smp_ops);
+
+	return 0;
+#else
+	return -ENODEV;
+#endif
+}
 
 #endif /* __ASM_SMP_OPS_H */

arch/mips/mipssim/sim_setup.c

@@ -59,18 +59,17 @@ void __init prom_init(void)
 
 	prom_meminit();
 
-#ifdef CONFIG_MIPS_MT_SMP
-	if (cpu_has_mipsmt)
-		register_smp_ops(&vsmp_smp_ops);
-	else
-		register_smp_ops(&up_smp_ops);
-#endif
+	if (cpu_has_mipsmt) {
+		if (!register_vsmp_smp_ops())
+			return;
+
 #ifdef CONFIG_MIPS_MT_SMTC
-	if (cpu_has_mipsmt)
 		register_smp_ops(&ssmtc_smp_ops);
-	else
-		register_smp_ops(&up_smp_ops);
+			return;
 #endif
+	}
+
+	register_up_smp_ops();
 }
 
 static void __init serial_init(void)

arch/mips/mti-malta/malta-init.c

@@ -28,6 +28,7 @@
 #include <asm/io.h>
 #include <asm/system.h>
 #include <asm/cacheflush.h>
+#include <asm/smp-ops.h>
 #include <asm/traps.h>
 
 #include <asm/gcmpregs.h>
@@ -358,15 +359,14 @@ void __init prom_init(void)
 #ifdef CONFIG_SERIAL_8250_CONSOLE
 	console_config();
 #endif
-#ifdef CONFIG_MIPS_CMP
 	/* Early detection of CMP support */
 	if (gcmp_probe(GCMP_BASE_ADDR, GCMP_ADDRSPACE_SZ))
-		register_smp_ops(&cmp_smp_ops);
-	else
-#endif
-#ifdef CONFIG_MIPS_MT_SMP
-		register_smp_ops(&vsmp_smp_ops);
-#endif
+		if (!register_cmp_smp_ops())
+			return;
+
+	if (!register_vsmp_smp_ops())
+		return;
+
 #ifdef CONFIG_MIPS_MT_SMTC
 	register_smp_ops(&msmtc_smp_ops);
 #endif

arch/mips/pmc-sierra/msp71xx/msp_setup.c

@@ -228,13 +228,11 @@ void __init prom_init(void)
 	 */
 	msp_serial_setup();
 
-#ifdef CONFIG_MIPS_MT_SMP
-	register_smp_ops(&vsmp_smp_ops);
-#endif
-
+	if (register_vsmp_smp_ops()) {
 #ifdef CONFIG_MIPS_MT_SMTC
-	register_smp_ops(&msp_smtc_smp_ops);
+		register_smp_ops(&msp_smtc_smp_ops);
 #endif
+	}
 
 #ifdef CONFIG_PMCTWILED
 	/*