diff --git a/lib/powerpc/asm/reg.h b/lib/powerpc/asm/reg.h
index d2ca964c4..12f9e8ac6 100644
--- a/lib/powerpc/asm/reg.h
+++ b/lib/powerpc/asm/reg.h
@@ -35,6 +35,7 @@
 #define SPR_HSRR1	0x13b
 #define SPR_LPCR	0x13e
 #define   LPCR_HDICE		UL(0x1)
+#define   LPCR_LD		UL(0x20000)
 #define SPR_HEIR	0x153
 #define SPR_MMCR0	0x31b
 #define   MMCR0_FC		UL(0x80000000)
diff --git a/powerpc/Makefile.common b/powerpc/Makefile.common
index b6f9b3b85..1348f658b 100644
--- a/powerpc/Makefile.common
+++ b/powerpc/Makefile.common
@@ -15,6 +15,7 @@ tests-common = \
 	$(TEST_DIR)/tm.elf \
 	$(TEST_DIR)/smp.elf \
 	$(TEST_DIR)/sprs.elf \
+	$(TEST_DIR)/timebase.elf \
 	$(TEST_DIR)/interrupts.elf
 
 tests-all = $(tests-common) $(tests)
diff --git a/powerpc/timebase.c b/powerpc/timebase.c
new file mode 100644
index 000000000..1908ca838
--- /dev/null
+++ b/powerpc/timebase.c
@@ -0,0 +1,329 @@
+/* SPDX-License-Identifier: LGPL-2.0-only */
+/*
+ * Test Timebase
+ *
+ * Copyright 2024 Nicholas Piggin, IBM Corp.
+ *
+ * This contains tests of timebase facility, TB, DEC, etc.
+ */
+#include <libcflat.h>
+#include <util.h>
+#include <migrate.h>
+#include <alloc.h>
+#include <asm/handlers.h>
+#include <devicetree.h>
+#include <asm/hcall.h>
+#include <asm/processor.h>
+#include <asm/time.h>
+#include <asm/barrier.h>
+
+static int dec_bits = 0;
+
+static void cpu_dec_bits(int fdtnode, u64 regval __unused, void *arg __unused)
+{
+	const struct fdt_property *prop;
+	int plen;
+
+	prop = fdt_get_property(dt_fdt(), fdtnode, "ibm,dec-bits", &plen);
+	if (!prop) {
+		dec_bits = 32;
+		return;
+	}
+
+	/* Sanity check for the property layout (first two bytes are header) */
+	assert(plen == 4);
+
+	dec_bits = fdt32_to_cpu(*(uint32_t *)prop->data);
+}
+
+/* Check amount of CPUs nodes that have the TM flag */
+static int find_dec_bits(void)
+{
+	int ret;
+
+	ret = dt_for_each_cpu_node(cpu_dec_bits, NULL);
+	if (ret < 0)
+		return ret;
+
+	return dec_bits;
+}
+
+
+static bool do_migrate = false;
+static volatile bool got_interrupt;
+static volatile struct pt_regs recorded_regs;
+
+static uint64_t dec_max;
+static uint64_t dec_min;
+
+static void test_tb(int argc, char **argv)
+{
+	uint64_t tb;
+
+	tb = get_tb();
+	if (do_migrate)
+		migrate();
+	report(get_tb() >= tb, "timebase is incrementing");
+}
+
+static void dec_stop_handler(struct pt_regs *regs, void *data)
+{
+	mtspr(SPR_DEC, dec_max);
+}
+
+static void dec_handler(struct pt_regs *regs, void *data)
+{
+	got_interrupt = true;
+	memcpy((void *)&recorded_regs, regs, sizeof(struct pt_regs));
+	regs->msr &= ~MSR_EE;
+}
+
+static void test_dec(int argc, char **argv)
+{
+	uint64_t tb1, tb2, dec;
+	int i;
+
+	handle_exception(0x900, &dec_handler, NULL);
+
+	for (i = 0; i < 100; i++) {
+		tb1 = get_tb();
+		mtspr(SPR_DEC, dec_max);
+		dec = mfspr(SPR_DEC);
+		tb2 = get_tb();
+		if (tb2 - tb1 < dec_max - dec)
+			break;
+	}
+	report(tb2 - tb1 >= dec_max - dec, "decrementer remains within TB after mtDEC");
+
+	tb1 = get_tb();
+	mtspr(SPR_DEC, dec_max);
+	mdelay(1000);
+	dec = mfspr(SPR_DEC);
+	tb2 = get_tb();
+	report(tb2 - tb1 >= dec_max - dec, "decrementer remains within TB after 1s");
+
+	mtspr(SPR_DEC, dec_max);
+	local_irq_enable();
+	local_irq_disable();
+	if (mfspr(SPR_DEC) <= dec_max) {
+		report(!got_interrupt, "no interrupt on decrementer positive");
+	}
+	got_interrupt = false;
+
+	mtspr(SPR_DEC, 1);
+	mdelay(100); /* Give the timer a chance to run */
+	if (do_migrate)
+		migrate();
+	local_irq_enable();
+	local_irq_disable();
+	report(got_interrupt, "interrupt on decrementer underflow");
+	got_interrupt = false;
+
+	if (do_migrate)
+		migrate();
+	local_irq_enable();
+	local_irq_disable();
+	report(got_interrupt, "interrupt on decrementer still underflown");
+	got_interrupt = false;
+
+	mtspr(SPR_DEC, 0);
+	mdelay(100); /* Give the timer a chance to run */
+	if (do_migrate)
+		migrate();
+	local_irq_enable();
+	local_irq_disable();
+	report(got_interrupt, "DEC deal with set to 0");
+	got_interrupt = false;
+
+	/* Test for level-triggered decrementer */
+	mtspr(SPR_DEC, -1ULL);
+	if (do_migrate)
+		migrate();
+	local_irq_enable();
+	local_irq_disable();
+	report(got_interrupt, "interrupt on decrementer write MSB");
+	got_interrupt = false;
+
+	mtspr(SPR_DEC, dec_max);
+	local_irq_enable();
+	if (do_migrate)
+		migrate();
+	mtspr(SPR_DEC, -1);
+	local_irq_disable();
+	report(got_interrupt, "interrupt on decrementer write MSB with irqs on");
+	got_interrupt = false;
+
+	mtspr(SPR_DEC, dec_min + 1);
+	mdelay(100);
+	local_irq_enable();
+	local_irq_disable();
+	report(!got_interrupt, "no interrupt after wrap to positive");
+	got_interrupt = false;
+
+	handle_exception(0x900, NULL, NULL);
+}
+
+static void test_hdec(int argc, char **argv)
+{
+	uint64_t tb1, tb2, hdec;
+
+	if (!machine_is_powernv()) {
+		report_skip("skipping on !powernv machine");
+		return;
+	}
+
+	handle_exception(0x900, &dec_stop_handler, NULL);
+	handle_exception(0x980, &dec_handler, NULL);
+
+	mtspr(SPR_HDEC, dec_max);
+	mtspr(SPR_LPCR, mfspr(SPR_LPCR) | LPCR_HDICE);
+
+	tb1 = get_tb();
+	mtspr(SPR_HDEC, dec_max);
+	hdec = mfspr(SPR_HDEC);
+	tb2 = get_tb();
+	report(tb2 - tb1 >= dec_max - hdec, "hdecrementer remains within TB");
+
+	tb1 = get_tb();
+	mtspr(SPR_HDEC, dec_max);
+	mdelay(1000);
+	hdec = mfspr(SPR_HDEC);
+	tb2 = get_tb();
+	report(tb2 - tb1 >= dec_max - hdec, "hdecrementer remains within TB after 1s");
+
+	mtspr(SPR_HDEC, dec_max);
+	local_irq_enable();
+	local_irq_disable();
+	if (mfspr(SPR_HDEC) <= dec_max) {
+		report(!got_interrupt, "no interrupt on decrementer positive");
+	}
+	got_interrupt = false;
+
+	mtspr(SPR_HDEC, 1);
+	mdelay(100); /* Give the timer a chance to run */
+	if (do_migrate)
+		migrate();
+	/* HDEC is edge triggered so ensure it still fires */
+	mtspr(SPR_HDEC, dec_max);
+	local_irq_enable();
+	local_irq_disable();
+	report(got_interrupt, "interrupt on hdecrementer underflow");
+	got_interrupt = false;
+
+	if (do_migrate)
+		migrate();
+	local_irq_enable();
+	local_irq_disable();
+	report(!got_interrupt, "no interrupt on hdecrementer still underflown");
+	got_interrupt = false;
+
+	mtspr(SPR_HDEC, -1ULL);
+	if (do_migrate)
+		migrate();
+	local_irq_enable();
+	local_irq_disable();
+	report(got_interrupt, "no interrupt on hdecrementer underflown write MSB");
+	got_interrupt = false;
+
+	mtspr(SPR_HDEC, 0);
+	mdelay(100); /* Give the timer a chance to run */
+	if (do_migrate)
+		migrate();
+	/* HDEC is edge triggered so ensure it still fires */
+	mtspr(SPR_HDEC, dec_max);
+	local_irq_enable();
+	local_irq_disable();
+	report(got_interrupt, "HDEC deal with set to 0");
+	got_interrupt = false;
+
+	mtspr(SPR_HDEC, dec_max);
+	local_irq_enable();
+	if (do_migrate)
+		migrate();
+	mtspr(SPR_HDEC, -1ULL);
+	local_irq_disable();
+	report(got_interrupt, "interrupt on hdecrementer write MSB with irqs on");
+	got_interrupt = false;
+
+	mtspr(SPR_HDEC, dec_max);
+	got_interrupt = false;
+	mtspr(SPR_HDEC, dec_min + 1);
+	if (do_migrate)
+		migrate();
+	mdelay(100);
+	local_irq_enable();
+	local_irq_disable();
+	report(got_interrupt, "got interrupt after wrap to positive");
+	got_interrupt = false;
+
+	mtspr(SPR_HDEC, -1ULL);
+	local_irq_enable();
+	local_irq_disable();
+	got_interrupt = false;
+	mtspr(SPR_HDEC, dec_min + 1000000);
+	if (do_migrate)
+		migrate();
+	mdelay(100);
+	mtspr(SPR_HDEC, -1ULL);
+	local_irq_enable();
+	local_irq_disable();
+	report(got_interrupt, "edge re-armed after wrap to positive");
+	got_interrupt = false;
+
+	mtspr(SPR_LPCR, mfspr(SPR_LPCR) & ~LPCR_HDICE);
+
+	handle_exception(0x900, NULL, NULL);
+	handle_exception(0x980, NULL, NULL);
+}
+
+struct {
+	const char *name;
+	void (*func)(int argc, char **argv);
+} hctests[] = {
+	{ "tb", test_tb },
+	{ "dec", test_dec },
+	{ "hdec", test_hdec },
+	{ NULL, NULL }
+};
+
+int main(int argc, char **argv)
+{
+	bool all;
+	int i;
+
+	all = argc == 1 || !strcmp(argv[1], "all");
+
+	for (i = 1; i < argc; i++) {
+		if (!strcmp(argv[i], "-w")) {
+			do_migrate = true;
+			if (!all && argc == 2)
+				all = true;
+		}
+	}
+
+	find_dec_bits();
+	dec_max = (1ULL << (dec_bits - 1)) - 1;
+	dec_min = (1ULL << (dec_bits - 1));
+
+	if (machine_is_powernv() && dec_bits > 32) {
+		mtspr(SPR_LPCR, mfspr(SPR_LPCR) | LPCR_LD);
+	}
+
+	report_prefix_push("timebase");
+
+	for (i = 0; hctests[i].name != NULL; i++) {
+		if (all || strcmp(argv[1], hctests[i].name) == 0) {
+			report_prefix_push(hctests[i].name);
+			hctests[i].func(argc, argv);
+			report_prefix_pop();
+		}
+	}
+
+	report_prefix_pop();
+
+	if (machine_is_powernv() && dec_bits > 32) {
+		mtspr(SPR_LPCR, mfspr(SPR_LPCR) & ~LPCR_LD);
+	}
+
+	return report_summary();
+}
diff --git a/powerpc/unittests.cfg b/powerpc/unittests.cfg
index 803a636cb..0be787f67 100644
--- a/powerpc/unittests.cfg
+++ b/powerpc/unittests.cfg
@@ -97,6 +97,14 @@ machine = pseries
 extra_params = -append "'migration -m'"
 groups = migration
 
+[timebase]
+file = timebase.elf
+
+[timebase-icount]
+file = timebase.elf
+accel = tcg
+extra_params = -icount shift=5
+
 [h_cede_tm]
 file = tm.elf
 machine = pseries
