[PATCH v3 4/8] drivers: arm_architected_timer: refactor for pbl compatibility

All ARMv8-A cores implement the 64bit wide generic timer CNTPCT[1]. Thus
the driver is the candidate for all AARCH64 SoCs to implement
PBL_CLOCKSOURCE compatibilty.

There is one catch though: the CNTFRQ_EL0 register[2] must be programmed
by the bootrom, barebox or the tf-a before the `arm_arch_timer_init`
call or the clocksource setup will return with -ENODEV. A later
re-initialization is also possible by calling `arm_arch_timer_init`
again.

[1]: See "ARM Architecture Reference Manual for A-profile architecture
(rev L.a)", chapter D12 "The Generic Timer in AArch64 state"
[2]: See "ARM Architecture Reference Manual for A-profile architecture
(rev L.a)", chapter D12.1.2.1 "Initializing and reading the system
effective frequency"

Signed-off-by: Stefan Kerkmann <[email protected]>
---
 .../include/asm/hardware/arm_architected_timer.h   | 21 +++++++++++++++++++
 drivers/clocksource/Makefile                       |  2 +-
 drivers/clocksource/arm_architected_timer.c        | 24 ++++++++++++++--------
 3 files changed, 38 insertions(+), 9 deletions(-)

diff --git a/arch/arm/include/asm/hardware/arm_architected_timer.h b/arch/arm/include/asm/hardware/arm_architected_timer.h
new file mode 100644
index 0000000000..e0c1fd84fd
--- /dev/null
+++ b/arch/arm/include/asm/hardware/arm_architected_timer.h
@@ -0,0 +1,21 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#ifndef __ASM_ARM_HARDWARE_ARCH_TIMER_H
+#define __ASM_ARM_HARDWARE_ARCH_TIMER_H
+
+#include <linux/types.h>
+
+/**
+ * arm_arch_timer_init() - Initialize the ARM architected timer as global
+ * clocksource
+ * @cntfrq: The timer frequency, if zero the frequency is read from the
+ *          CNTFRQ_EL0 register
+ *
+ * This function is meant to be called in a PBL constructor or in the driver
+ * probe function.
+ *
+ * Return: 0 on success, -ENODEV if the timer frequency can not be determined
+ */
+int arm_arch_timer_init(uint64_t cntfrq);
+
+#endif
diff --git a/drivers/clocksource/Makefile b/drivers/clocksource/Makefile
index dff8255650..0c92477247 100644
--- a/drivers/clocksource/Makefile
+++ b/drivers/clocksource/Makefile
@@ -13,7 +13,7 @@ obj-$(CONFIG_CLOCKSOURCE_ORION)   += orion.o
 obj-$(CONFIG_CLOCKSOURCE_UEMD)    += uemd.o
 obj-$(CONFIG_CLOCKSOURCE_ROCKCHIP)+= rk_timer.o
 obj-$(CONFIG_CLOCKSOURCE_ATMEL_PIT) += timer-atmel-pit.o
-obj-$(CONFIG_CLOCKSOURCE_ARM_ARCHITECTED_TIMER) += arm_architected_timer.o
+obj-pbl-$(CONFIG_CLOCKSOURCE_ARM_ARCHITECTED_TIMER) += arm_architected_timer.o
 ifneq ($(CONFIG_CPU_V8),y)
 CFLAGS_arm_architected_timer.o := -march=armv7-a
 endif
diff --git a/drivers/clocksource/arm_architected_timer.c b/drivers/clocksource/arm_architected_timer.c
index daced94c0e..ea5f5b8e05 100644
--- a/drivers/clocksource/arm_architected_timer.c
+++ b/drivers/clocksource/arm_architected_timer.c
@@ -9,6 +9,7 @@
 #include <linux/clk.h>
 #include <io.h>
 #include <asm/system.h>
+#include <asm/hardware/arm_architected_timer.h>
 
 static uint64_t arm_arch_clocksource_read(void)
 {
@@ -22,22 +23,29 @@ static struct clocksource cs = {
 	.priority = 70,
 };
 
-static int arm_arch_timer_probe(struct device *dev)
+int arm_arch_timer_init(uint64_t cntfrq)
 {
-	u32 cntfrq;
-	int ret;
-
-	/* Some platforms don't set CNTFRQ_EL0 before barebox */
-	ret = of_property_read_u32(dev->of_node, "clock-frequency", &cntfrq);
-
-	if (ret)
+	if (!cntfrq)
 		cntfrq = get_cntfrq();
 
+	if (!cntfrq)
+		return -ENODEV;
+
 	cs.mult = clocksource_hz2mult(cntfrq, cs.shift);
 
 	return init_clock(&cs);
 }
 
+static int arm_arch_timer_probe(struct device *dev)
+{
+	u32 cntfrq = 0;
+
+	/* Some platforms don't set CNTFRQ_EL0 before barebox */
+	of_property_read_u32(dev->of_node, "clock-frequency", &cntfrq);
+
+	return arm_arch_timer_init(cntfrq);
+}
+
 static struct of_device_id arm_arch_timer_dt_ids[] = {
 	{ .compatible = "arm,armv7-timer", },
 	{ .compatible = "arm,armv8-timer", },

-- 
2.47.3