arm64: Check if PSCI before calling SMCCC

[andrew]

Summary

As SMCCC depends on PSCI check if the latter is present before calling
the former. This fixes an issue where we may call into SMCCC when there
is no PSCI in the system causing a smccc_version assert to fail.

Reported by: stevek
Sponsored by: Arm Ltd

[emaste]

LGTM

[stevek]

Looks good, verified with the board where we had seen the issue.

sys/arm64/arm64/cpu_errata.c

 #include <sys/cdefs.h>
 #include <sys/param.h>
 #include <sys/kernel.h>
 #include <sys/pcpu.h>
 #include <sys/systm.h>
 
 #include <machine/cpu.h>
 
+#include <dev/psci/psci.h>
 #include <dev/psci/smccc.h>
 
 typedef void (cpu_quirk_install)(void);
 struct cpu_quirks {
         cpu_quirk_install *quirk_install;
         u_int           midr_mask;
         u_int           midr_value;
 #define CPU_QUIRK_POST_DEVICE   (1 << 0)  /* After device attach */
.midr_value =
                     CPU_ID_RAW(CPU_IMPL_CAVIUM, CPU_PART_THUNDERX_81XX, 0, 0),
                 .quirk_install = install_thunderx_bcast_tlbi_workaround,
         },
 };
 
 static void
 install_psci_bp_hardening(void)
 {
+        /* SMCCC depends on PSCI. If PSCI is missing so is SMCCC */
+        if (!psci_present)
+                return;
 
         if (smccc_arch_features(SMCCC_ARCH_WORKAROUND_1) != SMCCC_RET_SUCCESS)
                 return;
 
         PCPU_SET(bp_harden, smccc_arch_workaround_1);
 }
 
 static void
 install_ssbd_workaround(void)
 {
         char *env;
 
         if (PCPU_GET(cpuid) == 0) {
                 env = kern_getenv("kern.cfg.ssbd");
                 if (env != NULL) {
                         if (strcmp(env, "force-on") == 0) {
                                 ssbd_method = SSBD_FORCE_ON;
                         } else if (strcmp(env, "force-off") == 0) {
                                 ssbd_method = SSBD_FORCE_OFF;
                         }
                 }
         }
+
+        /* SMCCC depends on PSCI. If PSCI is missing so is SMCCC */
+        if (!psci_present)
+                return;
 
         /* Enable the workaround on this CPU if it's enabled in the firmware */
         if (smccc_arch_features(SMCCC_ARCH_WORKAROUND_2) != SMCCC_RET_SUCCESS)
                 return;
 
         switch(ssbd_method) {
         case SSBD_FORCE_ON:
                 smccc_arch_workaround_2(1);