Using the information presented by GTDT to initialize the arch
timer (not memory-mapped).

Originally-by: Amit Daniel Kachhap [off-list ref]
Signed-off-by: Hanjun Guo <redacted>
---
 arch/arm64/kernel/time.c             |    7 ++
 drivers/clocksource/arm_arch_timer.c |  117 ++++++++++++++++++++++++++++------
 include/linux/clocksource.h          |    6 ++
 3 files changed, 111 insertions(+), 19 deletions(-)

diff --git a/arch/arm64/kernel/time.c b/arch/arm64/kernel/time.c
index 1a7125c..42f9195 100644
--- a/arch/arm64/kernel/time.c
+++ b/arch/arm64/kernel/time.c

@@ -35,6 +35,7 @@
 #include <linux/delay.h>
 #include <linux/clocksource.h>
 #include <linux/clk-provider.h>
+#include <linux/acpi.h>
 
 #include <clocksource/arm_arch_timer.h>
 

@@ -72,6 +73,12 @@ void __init time_init(void)
 
 	tick_setup_hrtimer_broadcast();
 
+	/*
+	 * Since ACPI or FDT will only one be available in the system,
+	 * we can use acpi_generic_timer_init() here safely
+	 */
+	acpi_generic_timer_init();
+
 	arch_timer_rate = arch_timer_get_rate();
 	if (!arch_timer_rate)
 		panic("Unable to initialise architected timer.\n");

diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index 5163ec1..397783f 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c

@@ -21,6 +21,7 @@
 #include <linux/io.h>
 #include <linux/slab.h>
 #include <linux/sched_clock.h>
+#include <linux/acpi.h>
 
 #include <asm/arch_timer.h>
 #include <asm/virt.h>

@@ -338,8 +339,12 @@ arch_timer_detect_rate(void __iomem *cntbase, struct device_node *np)
 	if (arch_timer_rate)
 		return;
 
-	/* Try to determine the frequency from the device tree or CNTFRQ */
-	if (of_property_read_u32(np, "clock-frequency", &arch_timer_rate)) {
+	/*
+	 * Try to determine the frequency from the device tree or CNTFRQ,
+	 * if ACPI is enabled, get the frequency from CNTFRQ ONLY.
+	 */