src/arch/ppc64/arch_timer.c: implement timer functions

Change-Id: I4a244df01f6d15cbefb3b01079f6eec943136983
Signed-off-by: Michał Żygowski <michal.zygowski@3mdeb.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/57077
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Krystian Hebel <krystian.hebel@3mdeb.com>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>

src/arch/ppc64/Makefile.inc

@@ -34,6 +34,7 @@ endif
 ################################################################################
 ifeq ($(CONFIG_ARCH_ROMSTAGE_PPC64),y)
 
+romstage-y += arch_timer.c
 romstage-y += boot.c
 romstage-y += stages.c
 romstage-y += rom_media.c
@@ -64,6 +65,7 @@ ifeq ($(CONFIG_ARCH_RAMSTAGE_PPC64),y)
 
 ramstage-y += rom_media.c
 ramstage-y += stages.c
+ramstage-y += arch_timer.c
 ramstage-y += boot.c
 ramstage-y += tables.c
 ramstage-y += \

src/arch/ppc64/arch_timer.c

@@ -0,0 +1,41 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#include <timer.h>
+#include <delay.h>
+#include <cpu/power/spr.h>
+
+/* Refer to hostboot/src/kernel/timemgr.C */
+
+/* Time base frequency is 512 MHz so 512 ticks per usec */
+#define TB_TICKS_PER_USEC 512
+
+__weak void init_timer(void) { /* do nothing */ }
+
+static struct monotonic_counter {
+	int initialized;
+	struct mono_time time;
+	uint64_t last_value;
+} mono_counter;
+
+void timer_monotonic_get(struct mono_time *mt)
+{
+	uint64_t current_tick;
+	uint64_t usecs_elapsed;
+
+	if (!mono_counter.initialized) {
+		mono_counter.last_value = read_spr(SPR_TB);
+		mono_counter.initialized = 1;
+	}
+
+	current_tick = read_spr(SPR_TB);
+	usecs_elapsed = (current_tick - mono_counter.last_value) / TB_TICKS_PER_USEC;
+
+	/* Update current time and tick values only if a full tick occurred. */
+	if (usecs_elapsed) {
+		mono_time_add_usecs(&mono_counter.time, usecs_elapsed);
+		mono_counter.last_value = current_tick;
+	}
+
+	/* Save result. */
+	*mt = mono_counter.time;
+}