MIPS: pm-cps: Prevent use of mips_cps_* without CPS SMP

These symbols will not be defined when CONFIG_MIPS_CPS=n, but although
the CPS_PM_POWER_GATED state will never be used in that case the
compiler doesn't have enough information to figure that out. Add checks
which evaluate to a constant false for CONFIG_MIPS_CPS=n cases in order
to help the compiler out & eliminate the symbol references.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Reviewed-by: Markos Chandras <markos.chandras@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/7278/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

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

@@ -31,11 +31,19 @@ extern void mips_cps_core_init(void);
 
 extern struct vpe_boot_config *mips_cps_boot_vpes(void);
 
-extern bool mips_cps_smp_in_use(void);
-
 extern void mips_cps_pm_save(void);
 extern void mips_cps_pm_restore(void);
 
+#ifdef CONFIG_MIPS_CPS
+
+extern bool mips_cps_smp_in_use(void);
+
+#else /* !CONFIG_MIPS_CPS */
+
+static inline bool mips_cps_smp_in_use(void) { return false; }
+
+#endif /* !CONFIG_MIPS_CPS */
+
 #else /* __ASSEMBLY__ */
 
 .extern mips_cps_bootcfg;

arch/mips/kernel/pm-cps.c

@@ -149,6 +149,10 @@ int cps_pm_enter_state(enum cps_pm_state state)
 
 	/* Setup the VPE to run mips_cps_pm_restore when started again */
 	if (config_enabled(CONFIG_CPU_PM) && state == CPS_PM_POWER_GATED) {
+		/* Power gating relies upon CPS SMP */
+		if (!mips_cps_smp_in_use())
+			return -EINVAL;
+
 		core_cfg = &mips_cps_core_bootcfg[core];
 		vpe_cfg = &core_cfg->vpe_config[current_cpu_data.vpe_id];
 		vpe_cfg->pc = (unsigned long)mips_cps_pm_restore;
@@ -376,6 +380,10 @@ static void * __init cps_gen_entry_code(unsigned cpu, enum cps_pm_state state)
 	memset(relocs, 0, sizeof(relocs));
 
 	if (config_enabled(CONFIG_CPU_PM) && state == CPS_PM_POWER_GATED) {
+		/* Power gating relies upon CPS SMP */
+		if (!mips_cps_smp_in_use())
+			goto out_err;
+
 		/*
 		 * Save CPU state. Note the non-standard calling convention
 		 * with the return address placed in v0 to avoid clobbering