[PATCH v2 2/2] clocksource/drivers/mtk_systimer: Add support for Mediatek SoCs

[Stanley Chu]

This patch adds a new clock event for the timer
found on the Mediatek SoCs.

The Mediatek System Timer has several 32-bit timers.
Only one timer is used by this driver as a clock event
supporting oneshot events.

The System Timer can be run with two clocks. A 13 MHz system
clock and the RTC clock running at 32 KHz. This implementation
uses the system clock with no clock source divider.

The interrupts are shared between the different timers.
We just enable one interrupt for the clock event. The clock
event timer is used by all cores.

Signed-off-by: Stanley Chu <stanley.chu@xxxxxxxxxxxx>
---
 drivers/clocksource/Kconfig        |   13 +++-
 drivers/clocksource/Makefile       |    1 +
 drivers/clocksource/mtk_systimer.c |  132 ++++++++++++++++++++++++++++++++++++
 3 files changed, 144 insertions(+), 2 deletions(-)
 create mode 100644 drivers/clocksource/mtk_systimer.c

diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
index dec0dd8..362c110 100644
--- a/drivers/clocksource/Kconfig
+++ b/drivers/clocksource/Kconfig
@@ -442,12 +442,21 @@ config SYS_SUPPORTS_SH_CMT
         bool
 
 config MTK_TIMER
-	bool "Mediatek timer driver" if COMPILE_TEST
+	bool "Mediatek general purpose timer driver" if COMPILE_TEST
 	depends on HAS_IOMEM
 	select TIMER_OF
 	select CLKSRC_MMIO
 	help
-	  Support for Mediatek timer driver.
+	  Support for Mediatek General Purpose Timer (GPT) driver.
+
+config MTK_TIMER_SYSTIMER
+	bool "Mediatek system timer driver" if COMPILE_TEST
+	depends on HAS_IOMEM
+	select TIMER_OF
+	select CLKSRC_MMIO
+	help
+	  Support for Mediatek System Timer (sys_timer) driver used as
+	  a clock event supporting oneshot events.
 
 config SPRD_TIMER
 	bool "Spreadtrum timer driver" if EXPERT
diff --git a/drivers/clocksource/Makefile b/drivers/clocksource/Makefile
index 00caf37..cdd34b2 100644
--- a/drivers/clocksource/Makefile
+++ b/drivers/clocksource/Makefile
@@ -50,6 +50,7 @@ obj-$(CONFIG_FSL_FTM_TIMER)	+= fsl_ftm_timer.o
 obj-$(CONFIG_VF_PIT_TIMER)	+= vf_pit_timer.o
 obj-$(CONFIG_CLKSRC_QCOM)	+= qcom-timer.o
 obj-$(CONFIG_MTK_TIMER)		+= mtk_timer.o
+obj-$(CONFIG_MTK_TIMER_SYSTIMER)	+= mtk_systimer.o
 obj-$(CONFIG_CLKSRC_PISTACHIO)	+= time-pistachio.o
 obj-$(CONFIG_CLKSRC_TI_32K)	+= timer-ti-32k.o
 obj-$(CONFIG_CLKSRC_NPS)	+= timer-nps.o
diff --git a/drivers/clocksource/mtk_systimer.c b/drivers/clocksource/mtk_systimer.c
new file mode 100644
index 0000000..77161bb
--- /dev/null
+++ b/drivers/clocksource/mtk_systimer.c
@@ -0,0 +1,132 @@
+// SPDX-License-Identifier: GPL-2.0+
+//
+//  Copyright (C) 2018 MediaTek Inc.
+
+#include <linux/interrupt.h>
+#include <linux/irqreturn.h>
+#include <linux/clockchips.h>
+#include <linux/clocksource.h>
+#include <linux/io.h>
+#include "timer-of.h"
+
+/* registers */
+#define STMR_CON                  (0x0)
+#define STMR_VAL                  (0x4)
+
+#define TIMER_REG_CON(to)         (timer_of_base(to) + STMR_CON)
+#define TIMER_REG_VAL(to)         (timer_of_base(to) + STMR_VAL)
+
+/* STMR_CON */
+#define STMR_CON_EN               BIT(0)
+#define STMR_CON_IRQ_EN           BIT(1)
+#define STMR_CON_IRQ_CLR          BIT(4)
+
+#define TIMER_SYNC_TICKS          3
+
+static void mtk_stmr_reset(struct timer_of *to)
+{
+	/* Clear IRQ */
+	writel(STMR_CON_IRQ_CLR | STMR_CON_EN, TIMER_REG_CON(to));
+
+	/* Reset counter */
+	writel(0, TIMER_REG_VAL(to));
+
+	/* Disable timer */
+	writel(0, TIMER_REG_CON(to));
+}
+
+static void mtk_stmr_ack_irq(struct timer_of *to)
+{
+	mtk_stmr_reset(to);
+}
+
+static irqreturn_t mtk_stmr_handler(int irq, void *dev_id)
+{
+	struct clock_event_device *clkevt = (struct clock_event_device *)dev_id;
+	struct timer_of *to = to_timer_of(clkevt);
+
+	mtk_stmr_ack_irq(to);
+	clkevt->event_handler(clkevt);
+
+	return IRQ_HANDLED;
+}
+
+static int mtk_stmr_clkevt_next_event(unsigned long ticks,
+				      struct clock_event_device *clkevt)
+{
+	struct timer_of *to = to_timer_of(clkevt);
+
+	/*
+	 * reset timer first because we do not expect interrupt is triggered
+	 * by old compare value.
+	 */
+	mtk_stmr_reset(to);
+
+	writel(STMR_CON_EN, TIMER_REG_CON(to));
+
+	writel(ticks, TIMER_REG_VAL(to));
+
+	writel(STMR_CON_EN | STMR_CON_IRQ_EN, TIMER_REG_CON(to));
+
+	return 0;
+}
+
+static int mtk_stmr_clkevt_shutdown(struct clock_event_device *clkevt)
+{
+	mtk_stmr_reset(to_timer_of(clkevt));
+
+	return 0;
+}
+
+static int mtk_stmr_clkevt_resume(struct clock_event_device *clkevt)
+{
+	return mtk_stmr_clkevt_shutdown(clkevt);
+}
+
+static int mtk_stmr_clkevt_oneshot(struct clock_event_device *clkevt)
+{
+	return 0;
+}
+
+static struct timer_of to = {
+	.flags = TIMER_OF_IRQ | TIMER_OF_BASE | TIMER_OF_CLOCK,
+
+	.clkevt = {
+		.name = "mtk-clkevt",
+		.rating = 300,
+		.features = CLOCK_EVT_FEAT_DYNIRQ | CLOCK_EVT_FEAT_ONESHOT,
+		.set_state_shutdown = mtk_stmr_clkevt_shutdown,
+		.set_state_oneshot = mtk_stmr_clkevt_oneshot,
+		.tick_resume = mtk_stmr_clkevt_resume,
+		.set_next_event = mtk_stmr_clkevt_next_event,
+		.cpumask = cpu_possible_mask,
+	},
+
+	.of_irq = {
+		.handler = mtk_stmr_handler,
+		.flags = IRQF_TIMER | IRQF_IRQPOLL | IRQF_TRIGGER_HIGH |
+			 IRQF_PERCPU,
+	},
+};
+
+static int __init mtk_stmr_init(struct device_node *node)
+{
+	int ret;
+
+	ret = timer_of_init(node, &to);
+	if (ret)
+		return ret;
+
+	mtk_stmr_reset(&to);
+
+	clockevents_config_and_register(&to.clkevt, timer_of_rate(&to),
+					TIMER_SYNC_TICKS, 0xffffffff);
+
+	pr_info("mtk_stmr: irq=%d, rate=%lu, max_ns: %llu, min_ns: %llu\n",
+		timer_of_irq(&to), timer_of_rate(&to),
+		to.clkevt.max_delta_ns, to.clkevt.min_delta_ns);
+
+	return ret;
+}
+
+TIMER_OF_DECLARE(mtk_systimer, "mediatek,sys_timer", mtk_stmr_init);
-- 
1.7.9.5