powerpc/64: Fix watchdog configuration regressions

This fixes a couple more bits of fallout from the new hard lockup watchdog
patch.

It restores the required hw_nmi_get_sample_period() function for the
perf watchdog, and removes some function declarations on 64e that are only
defined for 64s. This fixes the 64e build when the hardlockup detector is
enabled.

It restores the default behaviour of disabling the perf watchdog, and also
fixes disabling the 64s watchdog when running as a guest.

Fixes: 2104180a53 ("powerpc/64s: implement arch-specific hardlockup watchdog")
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kernel/setup_64.c

@@ -756,3 +756,31 @@ unsigned long memory_block_size_bytes(void)
 struct ppc_pci_io ppc_pci_io;
 EXPORT_SYMBOL(ppc_pci_io);
 #endif
+
+#ifdef CONFIG_HARDLOCKUP_DETECTOR_PERF
+u64 hw_nmi_get_sample_period(int watchdog_thresh)
+{
+	return ppc_proc_freq * watchdog_thresh;
+}
+#endif
+
+/*
+ * The perf based hardlockup detector breaks PMU event based branches, so
+ * disable it by default. Book3S has a soft-nmi hardlockup detector based
+ * on the decrementer interrupt, so it does not suffer from this problem.
+ *
+ * It is likely to get false positives in VM guests, so disable it there
+ * by default too.
+ */
+static int __init disable_hardlockup_detector(void)
+{
+#ifdef CONFIG_HARDLOCKUP_DETECTOR_PERF
+	hardlockup_detector_disable();
+#else
+	if (firmware_has_feature(FW_FEATURE_LPAR))
+		hardlockup_detector_disable();
+#endif
+
+	return 0;
+}
+early_initcall(disable_hardlockup_detector);