clk: renesas: r9a06g032: Add restart handler

The SYSCTRL module also does reset handling. Start supporting that by
allowing software resets which can then be utilized by a restart
handler. Finally 'reboot' will do something useful on RZ/N1D. Watchdog
support to be added later.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/20241128091113.24116-2-wsa+renesas@sang-engineering.com
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>

Author: Wolfram Sang

drivers/clk/renesas/r9a06g032-clocks.c

@@ -20,6 +20,7 @@
 #include <linux/platform_device.h>
 #include <linux/pm_clock.h>
 #include <linux/pm_domain.h>
+#include <linux/reboot.h>
 #include <linux/slab.h>
 #include <linux/soc/renesas/r9a06g032-sysctrl.h>
 #include <linux/spinlock.h>
@@ -29,6 +30,14 @@
 #define R9A06G032_SYSCTRL_USB_H2MODE  (1<<1)
 #define R9A06G032_SYSCTRL_DMAMUX 0xA0
 
+#define R9A06G032_SYSCTRL_RSTEN 0x120
+#define R9A06G032_SYSCTRL_RSTEN_MRESET_EN BIT(0)
+#define R9A06G032_SYSCTRL_RSTCTRL 0x198
+/* These work for both reset registers */
+#define R9A06G032_SYSCTRL_SWRST BIT(6)
+#define R9A06G032_SYSCTRL_WDA7RST_1 BIT(2)
+#define R9A06G032_SYSCTRL_WDA7RST_0 BIT(1)
+
 /**
  * struct regbit - describe one bit in a register
  * @reg: offset of register relative to base address,
@@ -1270,6 +1279,12 @@ static void r9a06g032_clocks_del_clk_provider(void *data)
 	of_clk_del_provider(data);
 }
 
+static int r9a06g032_restart_handler(struct sys_off_data *data)
+{
+	writel(R9A06G032_SYSCTRL_SWRST, sysctrl_priv->reg + R9A06G032_SYSCTRL_RSTCTRL);
+	return NOTIFY_DONE;
+}
+
 static void __init r9a06g032_init_h2mode(struct r9a06g032_priv *clocks)
 {
 	struct device_node *usbf_np;
@@ -1324,6 +1339,18 @@ static int __init r9a06g032_clocks_probe(struct platform_device *pdev)
 
 	r9a06g032_init_h2mode(clocks);
 
+	/* Clear potentially pending resets */
+	writel(R9A06G032_SYSCTRL_WDA7RST_0 | R9A06G032_SYSCTRL_WDA7RST_1,
+	       clocks->reg + R9A06G032_SYSCTRL_RSTCTRL);
+	/* Allow software reset */
+	writel(R9A06G032_SYSCTRL_SWRST | R9A06G032_SYSCTRL_RSTEN_MRESET_EN,
+	       clocks->reg + R9A06G032_SYSCTRL_RSTEN);
+
+	error = devm_register_sys_off_handler(dev, SYS_OFF_MODE_RESTART, SYS_OFF_PRIO_HIGH,
+					      r9a06g032_restart_handler, NULL);
+	if (error)
+		dev_warn(dev, "couldn't register restart handler (%d)\n", error);
+
 	for (i = 0; i < ARRAY_SIZE(r9a06g032_clocks); ++i) {
 		const struct r9a06g032_clkdesc *d = &r9a06g032_clocks[i];
 		const char *parent_name = d->source ?