[PATCH v2 3/4] clocksource/drivers/timer-vt8500: Add watchdog functionality

[Alexey Charkov <alchark@gmail.com>]

VIA/WonderMedia system timer IP can generate a watchdog reset when its
clocksource counter matches the value in the match register 0 and
watchdog function is enabled. For this to work, obvously the clock event
device must use a different match register (1~3) and respective interrupt.

Check if at least two interrupts are provided by the device tree, then use
match register 1 for system clock events and match register 0 for watchdog
respectively.

Signed-off-by: Alexey Charkov <alchark@gmail.com>
---
 drivers/clocksource/Kconfig        | 11 +++++++
 drivers/clocksource/timer-vt8500.c | 61 ++++++++++++++++++++++++++++++++++----
 2 files changed, 67 insertions(+), 5 deletions(-)

diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
index 487c8525996724fbf9c6e9726dabb478d86513b9..8f5e41ff23386d9ecb46b38603dae485db71cfc7 100644
--- a/drivers/clocksource/Kconfig
+++ b/drivers/clocksource/Kconfig
@@ -181,6 +181,17 @@ config VT8500_TIMER
 	help
 	  Enables support for the VT8500 driver.
 
+config VT8500_TIMER_WATCHDOG
+	bool "Enable VT8500 watchdog functionality"
+	depends on VT8500_TIMER
+	depends on WATCHDOG && WATCHDOG_CORE=y
+	help
+	  VIA/WonderMedia SoCs can use their system timer as a hardware
+	  watchdog, as long as the first timer channel is free from other
+	  uses and respective function is enabled in its registers. To
+	  make use of it, say Y here and ensure that the device tree
+	  lists at least two interrupts for the VT8500 timer device
+
 config NPCM7XX_TIMER
 	bool "NPCM7xx timer driver" if COMPILE_TEST
 	depends on HAS_IOMEM
diff --git a/drivers/clocksource/timer-vt8500.c b/drivers/clocksource/timer-vt8500.c
index 9f28f30dcaf83ab4e9c89952175b0d4c75bd6b40..4128c4f19adc2e02b6df2d0aa2dca4659f62fba7 100644
--- a/drivers/clocksource/timer-vt8500.c
+++ b/drivers/clocksource/timer-vt8500.c
@@ -22,6 +22,8 @@
 #include <linux/of_address.h>
 #include <linux/of_irq.h>
 
+#include <linux/watchdog.h>
+
 #define VT8500_TIMER_OFFSET	0x0100
 #define VT8500_TIMER_HZ		3000000
 
@@ -55,6 +57,9 @@
 #define MIN_OSCR_DELTA		16
 
 static void __iomem *regbase;
+static unsigned int sys_timer_ch;	 /* which match register to use
+					  * for the system timer
+					  */
 
 static u64 vt8500_timer_read(struct clocksource *cs)
 {
@@ -81,15 +86,15 @@ static int vt8500_timer_set_next_event(unsigned long cycles,
 	int loops = msecs_to_loops(10);
 	u64 alarm = clocksource.read(&clocksource) + cycles;
 
-	while (readl(regbase + TIMER_ACC_STS_REG) & TIMER_ACC_WR_MATCH(0)
+	while (readl(regbase + TIMER_ACC_STS_REG) & TIMER_ACC_WR_MATCH(sys_timer_ch)
 	       && --loops)
 		cpu_relax();
-	writel((unsigned long)alarm, regbase + TIMER_MATCH_REG(0));
+	writel((unsigned long)alarm, regbase + TIMER_MATCH_REG(sys_timer_ch));
 
 	if ((signed)(alarm - clocksource.read(&clocksource)) <= MIN_OSCR_DELTA)
 		return -ETIME;
 
-	writel(TIMER_INT_EN_MATCH(0), regbase + TIMER_INT_EN_REG);
+	writel(TIMER_INT_EN_MATCH(sys_timer_ch), regbase + TIMER_INT_EN_REG);
 
 	return 0;
 }
@@ -120,6 +125,40 @@ static irqreturn_t vt8500_timer_interrupt(int irq, void *dev_id)
 	return IRQ_HANDLED;
 }
 
+static int vt8500_watchdog_start(struct watchdog_device *wdd)
+{
+	u64 cycles = wdd->timeout * VT8500_TIMER_HZ;
+	u64 deadline = clocksource.read(&clocksource) + cycles;
+
+	writel((u32)deadline, regbase + TIMER_MATCH_REG(0));
+	writel(TIMER_WD_EN, regbase + TIMER_WATCHDOG_EN_REG);
+	return 0;
+}
+
+static int vt8500_watchdog_stop(struct watchdog_device *wdd)
+{
+	writel(0, regbase + TIMER_WATCHDOG_EN_REG);
+	return 0;
+}
+
+static const struct watchdog_ops vt8500_watchdog_ops = {
+	.start			= vt8500_watchdog_start,
+	.stop			= vt8500_watchdog_stop,
+};
+
+static const struct watchdog_info vt8500_watchdog_info = {
+	.identity		= "VIA VT8500 watchdog",
+	.options		= WDIOF_MAGICCLOSE |
+				  WDIOF_KEEPALIVEPING |
+				  WDIOF_SETTIMEOUT,
+};
+
+static struct watchdog_device vt8500_watchdog_device = {
+	.ops			= &vt8500_watchdog_ops,
+	.info			= &vt8500_watchdog_info,
+	.max_hw_heartbeat_ms	= -1UL / (VT8500_TIMER_HZ / 1000),
+};
+
 static int __init vt8500_timer_init(struct device_node *np)
 {
 	int timer_irq, ret;
@@ -131,7 +170,9 @@ static int __init vt8500_timer_init(struct device_node *np)
 		return -ENXIO;
 	}
 
-	timer_irq = irq_of_parse_and_map(np, 0);
+	sys_timer_ch = of_irq_count(np) > 1 ? 1 : 0;
+
+	timer_irq = irq_of_parse_and_map(np, sys_timer_ch);
 	if (!timer_irq) {
 		pr_err("%s: Missing irq description in Device Tree\n",
 								__func__);
@@ -140,7 +181,7 @@ static int __init vt8500_timer_init(struct device_node *np)
 
 	writel(TIMER_CTRL_ENABLE, regbase + TIMER_CTRL_REG);
 	writel(TIMER_STATUS_CLEARALL, regbase + TIMER_STATUS_REG);
-	writel(~0, regbase + TIMER_MATCH_REG(0));
+	writel(~0, regbase + TIMER_MATCH_REG(sys_timer_ch));
 
 	ret = clocksource_register_hz(&clocksource, VT8500_TIMER_HZ);
 	if (ret) {
@@ -163,6 +204,16 @@ static int __init vt8500_timer_init(struct device_node *np)
 	clockevents_config_and_register(&clockevent, VT8500_TIMER_HZ,
 					MIN_OSCR_DELTA * 2, 0xf0000000);
 
+	if (!IS_ENABLED(CONFIG_VT8500_TIMER_WATCHDOG))
+		return 0;
+
+	if (!sys_timer_ch) {
+		pr_info("%s: Not enabling watchdog: only one irq was given\n",
+			__func__);
+	} else {
+		watchdog_register_device(&vt8500_watchdog_device);
+	}
+
 	return 0;
 }
 

-- 
2.49.0