[PATCH v2 1/1] arm64: Early boot time stamps

[Pavel Tatashin]

Allow printk time stamps/sched_clock() to be available from the early
boot.

Signed-off-by: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
---
 arch/arm64/kernel/setup.c            | 25 +++++++++++++++++++++++++
 drivers/clocksource/arm_arch_timer.c |  8 ++++----
 include/clocksource/arm_arch_timer.h |  3 +++
 3 files changed, 32 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
index f4fc1e0544b7..7a43e63b737b 100644
--- a/arch/arm64/kernel/setup.c
+++ b/arch/arm64/kernel/setup.c
@@ -40,6 +40,7 @@
 #include <linux/efi.h>
 #include <linux/psci.h>
 #include <linux/sched/task.h>
+#include <linux/sched_clock.h>
 #include <linux/mm.h>
 
 #include <asm/acpi.h>
@@ -279,8 +280,32 @@ arch_initcall(reserve_memblock_reserved_regions);
 
 u64 __cpu_logical_map[NR_CPUS] = { [0 ... NR_CPUS-1] = INVALID_HWID };
 
+/*
+ * Get time stamps available early in boot, useful to identify boot time issues
+ * from the early boot.
+ */
+static __init void sched_clock_early_init(void)
+{
+	u64 freq = arch_timer_get_cntfrq();
+
+	/*
+	 * The arm64 boot protocol mandates that CNTFRQ_EL0 reflects
+	 * the timer frequency. To avoid breakage on misconfigured
+	 * systems, do not register the early sched_clock if the
+	 * programmed value if zero. Other random values will just
+	 * result in random output.
+	 */
+	if (!freq)
+		return;
+
+	arch_timer_read_counter = arch_counter_get_cntvct;
+	sched_clock_register(arch_timer_read_counter, ARCH_TIMER_NBITS, freq);
+}
+
 void __init setup_arch(char **cmdline_p)
 {
+	sched_clock_early_init();
+
 	init_mm.start_code = (unsigned long) _text;
 	init_mm.end_code   = (unsigned long) _etext;
 	init_mm.end_data   = (unsigned long) _edata;
diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index 9a7d4dc00b6e..e4843ad48bd3 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -175,13 +175,13 @@ static struct clocksource clocksource_counter = {
 	.name	= "arch_sys_counter",
 	.rating	= 400,
 	.read	= arch_counter_read,
-	.mask	= CLOCKSOURCE_MASK(56),
+	.mask	= CLOCKSOURCE_MASK(ARCH_TIMER_NBITS),
 	.flags	= CLOCK_SOURCE_IS_CONTINUOUS,
 };
 
 static struct cyclecounter cyclecounter __ro_after_init = {
 	.read	= arch_counter_read_cc,
-	.mask	= CLOCKSOURCE_MASK(56),
+	.mask	= CLOCKSOURCE_MASK(ARCH_TIMER_NBITS),
 };
 
 struct ate_acpi_oem_info {
@@ -963,8 +963,8 @@ static void __init arch_counter_register(unsigned type)
 	timecounter_init(&arch_timer_kvm_info.timecounter,
 			 &cyclecounter, start_count);
 
-	/* 56 bits minimum, so we assume worst case rollover */
-	sched_clock_register(arch_timer_read_counter, 56, arch_timer_rate);
+	sched_clock_register(arch_timer_read_counter, ARCH_TIMER_NBITS,
+			     arch_timer_rate);
 }
 
 static void arch_timer_stop(struct clock_event_device *clk)
diff --git a/include/clocksource/arm_arch_timer.h b/include/clocksource/arm_arch_timer.h
index 349e5957c949..c485512e1d01 100644
--- a/include/clocksource/arm_arch_timer.h
+++ b/include/clocksource/arm_arch_timer.h
@@ -71,6 +71,9 @@ enum arch_timer_spi_nr {
 #define ARCH_TIMER_EVT_STREAM_FREQ				\
 	(USEC_PER_SEC / ARCH_TIMER_EVT_STREAM_PERIOD_US)
 
+/* 56 bits minimum, so we assume worst case rollover */
+#define	ARCH_TIMER_NBITS		56
+
 struct arch_timer_kvm_info {
 	struct timecounter timecounter;
 	int virtual_irq;
-- 
2.19.1