watchdog: ixp4xx: Rewrite driver to use core

This rewrites the IXP4xx watchdog driver as follows:

- Spawn the watchdog driver as a platform device from the timer
  driver. It's one device in the hardware, and the fact that
  Linux splits the handling into two different devices is
  a Linux pecularity, and thus it becomes a Linux pecularity
  to spawn a separate watchdog driver.

- Spawn the watchdog driver from the timer driver at probe().
  This is well after the timer driver as actually registered and
  started and we know the register base is available.

- Instead of looping back callbacks to the timer drivers for all
  watchdog calls, pass the register base to the watchdog driver
  and manage the registers there. The two drivers aren't even
  interested in the same register so the spinlock is totally
  surplus, delete it.

- Replace pretty much all of the content in the watchdog driver
  with a simple, modern watchdog driver utilizing the watchdog
  core instead of registering its own misc device and ioctl()
  handling.

- Drop module parameters as the same already exist in the
  watchdog core.

What remains is a slim elegant (IMO) watchdog driver using the
watchdog core, spawning from device tree or boardfile alike.

Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20210726121214.2572836-1-linus.walleij@linaro.org
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>

drivers/clocksource/timer-ixp4xx.c

@@ -18,6 +18,7 @@
 #include <linux/delay.h>
 #include <linux/of_address.h>
 #include <linux/of_irq.h>
+#include <linux/platform_device.h>
 /* Goes away with OF conversion */
 #include <linux/platform_data/timer-ixp4xx.h>
 
@@ -29,9 +30,6 @@
 #define IXP4XX_OSRT1_OFFSET	0x08  /* Timer 1 Reload */
 #define IXP4XX_OST2_OFFSET	0x0C  /* Timer 2 Timestamp */
 #define IXP4XX_OSRT2_OFFSET	0x10  /* Timer 2 Reload */
-#define IXP4XX_OSWT_OFFSET	0x14  /* Watchdog Timer */
-#define IXP4XX_OSWE_OFFSET	0x18  /* Watchdog Enable */
-#define IXP4XX_OSWK_OFFSET	0x1C  /* Watchdog Key */
 #define IXP4XX_OSST_OFFSET	0x20  /* Timer Status */
 
 /*
@@ -45,17 +43,10 @@
 #define IXP4XX_OSST_TIMER_1_PEND	0x00000001
 #define IXP4XX_OSST_TIMER_2_PEND	0x00000002
 #define IXP4XX_OSST_TIMER_TS_PEND	0x00000004
-#define IXP4XX_OSST_TIMER_WDOG_PEND	0x00000008
-#define IXP4XX_OSST_TIMER_WARM_RESET	0x00000010
-
-#define	IXP4XX_WDT_KEY			0x0000482E
-#define	IXP4XX_WDT_RESET_ENABLE		0x00000001
-#define	IXP4XX_WDT_IRQ_ENABLE		0x00000002
-#define	IXP4XX_WDT_COUNT_ENABLE		0x00000004
+/* Remaining registers are for the watchdog and defined in the watchdog driver */
 
 struct ixp4xx_timer {
 	void __iomem *base;
-	unsigned int tick_rate;
 	u32 latch;
 	struct clock_event_device clkevt;
 #ifdef CONFIG_ARM
@@ -181,7 +172,6 @@ static __init int ixp4xx_timer_register(void __iomem *base,
 	if (!tmr)
 		return -ENOMEM;
 	tmr->base = base;
-	tmr->tick_rate = timer_freq;
 
 	/*
 	 * The timer register doesn't allow to specify the two least
@@ -239,6 +229,40 @@ static __init int ixp4xx_timer_register(void __iomem *base,
 	return 0;
 }
 
+static struct platform_device ixp4xx_watchdog_device = {
+	.name = "ixp4xx-watchdog",
+	.id = -1,
+};
+
+/*
+ * This probe gets called after the timer is already up and running. The main
+ * function on this platform is to spawn the watchdog device as a child.
+ */
+static int ixp4xx_timer_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+
+	/* Pass the base address as platform data and nothing else */
+	ixp4xx_watchdog_device.dev.platform_data = local_ixp4xx_timer->base;
+	ixp4xx_watchdog_device.dev.parent = dev;
+	return platform_device_register(&ixp4xx_watchdog_device);
+}
+
+static const struct of_device_id ixp4xx_timer_dt_id[] = {
+	{ .compatible = "intel,ixp4xx-timer", },
+	{ /* sentinel */ },
+};
+
+static struct platform_driver ixp4xx_timer_driver = {
+	.probe  = ixp4xx_timer_probe,
+	.driver = {
+		.name = "ixp4xx-timer",
+		.of_match_table = ixp4xx_timer_dt_id,
+		.suppress_bind_attrs = true,
+	},
+};
+builtin_platform_driver(ixp4xx_timer_driver);
+
 /**
  * ixp4xx_timer_setup() - Timer setup function to be called from boardfiles
  * @timerbase: physical base of timer block

drivers/watchdog/Kconfig

@@ -475,6 +475,7 @@ config FTWDT010_WATCHDOG
 config IXP4XX_WATCHDOG
 	tristate "IXP4xx Watchdog"
 	depends on ARCH_IXP4XX
+	select WATCHDOG_CORE
 	help
 	  Say Y here if to include support for the watchdog timer
 	  in the Intel IXP4xx network processors. This driver can