[v7,2/2] watchdog: Add Renesas RZ/N1 Watchdog driver

From: Phil Edworthy <phil.edworthy@renesas.com>

This is a driver for the standard WDT on the RZ/N1 devices. This WDT has
very limited timeout capabilities. However, it can reset the device.
To do so, the corresponding bits in the SysCtrl RSTEN register need to
be enabled. This is not done by this driver.

Signed-off-by: Phil Edworthy <phil.edworthy@renesas.com>
Signed-off-by: Jean-Jacques Hiblot <jjhiblot@traphandler.com>
Reviewed-by: Tzung-Bi Shih <tzungbi@kernel.org>
---
 drivers/watchdog/Kconfig    |   8 ++
 drivers/watchdog/Makefile   |   1 +
 drivers/watchdog/rzn1_wdt.c | 203 ++++++++++++++++++++++++++++++++++++
 3 files changed, 212 insertions(+)
 create mode 100644 drivers/watchdog/rzn1_wdt.c

On Wed, Apr 27, 2022 at 03:55:31PM +0200, Jean-Jacques Hiblot wrote:
> From: Phil Edworthy <phil.edworthy@renesas.com>
> 
> This is a driver for the standard WDT on the RZ/N1 devices. This WDT has
> very limited timeout capabilities. However, it can reset the device.
> To do so, the corresponding bits in the SysCtrl RSTEN register need to
> be enabled. This is not done by this driver.
> 
> Signed-off-by: Phil Edworthy <phil.edworthy@renesas.com>
> Signed-off-by: Jean-Jacques Hiblot <jjhiblot@traphandler.com>
> Reviewed-by: Tzung-Bi Shih <tzungbi@kernel.org>

Reviewed-by: Guenter Roeck <linux@roeck-us.net>

> ---
>  drivers/watchdog/Kconfig    |   8 ++
>  drivers/watchdog/Makefile   |   1 +
>  drivers/watchdog/rzn1_wdt.c | 203 ++++++++++++++++++++++++++++++++++++
>  3 files changed, 212 insertions(+)
>  create mode 100644 drivers/watchdog/rzn1_wdt.c
> 
> diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig
> index c4e82a8d863f..4d5e503c8950 100644
> --- a/drivers/watchdog/Kconfig
> +++ b/drivers/watchdog/Kconfig
> @@ -883,6 +883,14 @@ config RENESAS_RZAWDT
>  	  This driver adds watchdog support for the integrated watchdogs in the
>  	  Renesas RZ/A SoCs. These watchdogs can be used to reset a system.
>  
> +config RENESAS_RZN1WDT
> +	tristate "Renesas RZ/N1 watchdog"
> +	depends on ARCH_RENESAS || COMPILE_TEST
> +	select WATCHDOG_CORE
> +	help
> +	  This driver adds watchdog support for the integrated watchdogs in the
> +	  Renesas RZ/N1 SoCs. These watchdogs can be used to reset a system.
> +
>  config RENESAS_RZG2LWDT
>  	tristate "Renesas RZ/G2L WDT Watchdog"
>  	depends on ARCH_RENESAS || COMPILE_TEST
> diff --git a/drivers/watchdog/Makefile b/drivers/watchdog/Makefile
> index f7da867e8782..38d38564f47b 100644
> --- a/drivers/watchdog/Makefile
> +++ b/drivers/watchdog/Makefile
> @@ -84,6 +84,7 @@ obj-$(CONFIG_LPC18XX_WATCHDOG) += lpc18xx_wdt.o
>  obj-$(CONFIG_BCM7038_WDT) += bcm7038_wdt.o
>  obj-$(CONFIG_RENESAS_WDT) += renesas_wdt.o
>  obj-$(CONFIG_RENESAS_RZAWDT) += rza_wdt.o
> +obj-$(CONFIG_RENESAS_RZN1WDT) += rzn1_wdt.o
>  obj-$(CONFIG_RENESAS_RZG2LWDT) += rzg2l_wdt.o
>  obj-$(CONFIG_ASPEED_WATCHDOG) += aspeed_wdt.o
>  obj-$(CONFIG_STM32_WATCHDOG) += stm32_iwdg.o
> diff --git a/drivers/watchdog/rzn1_wdt.c b/drivers/watchdog/rzn1_wdt.c
> new file mode 100644
> index 000000000000..55ab384b9965
> --- /dev/null
> +++ b/drivers/watchdog/rzn1_wdt.c
> @@ -0,0 +1,203 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Renesas RZ/N1 Watchdog timer.
> + * This is a 12-bit timer driver from a (62.5/16384) MHz clock. It can't even
> + * cope with 2 seconds.
> + *
> + * Copyright 2018 Renesas Electronics Europe Ltd.
> + *
> + * Derived from Ralink RT288x watchdog timer.
> + */
> +
> +#include <linux/clk.h>
> +#include <linux/interrupt.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/of_address.h>
> +#include <linux/of_irq.h>
> +#include <linux/platform_device.h>
> +#include <linux/reboot.h>
> +#include <linux/watchdog.h>
> +
> +#define DEFAULT_TIMEOUT		60
> +
> +#define RZN1_WDT_RETRIGGER			0x0
> +#define RZN1_WDT_RETRIGGER_RELOAD_VAL		0
> +#define RZN1_WDT_RETRIGGER_RELOAD_VAL_MASK	0xfff
> +#define RZN1_WDT_RETRIGGER_PRESCALE		BIT(12)
> +#define RZN1_WDT_RETRIGGER_ENABLE		BIT(13)
> +#define RZN1_WDT_RETRIGGER_WDSI			(0x2 << 14)
> +
> +#define RZN1_WDT_PRESCALER			16384
> +#define RZN1_WDT_MAX				4095
> +
> +struct rzn1_watchdog {
> +	struct watchdog_device		wdtdev;
> +	void __iomem			*base;
> +	unsigned long			clk_rate_khz;
> +};
> +
> +static inline uint32_t max_heart_beat_ms(unsigned long clk_rate_khz)
> +{
> +	return (RZN1_WDT_MAX * RZN1_WDT_PRESCALER) / clk_rate_khz;
> +}
> +
> +static inline uint32_t compute_reload_value(uint32_t tick_ms,
> +					    unsigned long clk_rate_khz)
> +{
> +	return (tick_ms * clk_rate_khz) / RZN1_WDT_PRESCALER;
> +}
> +
> +static int rzn1_wdt_ping(struct watchdog_device *w)
> +{
> +	struct rzn1_watchdog *wdt = watchdog_get_drvdata(w);
> +
> +	/* Any value retrigggers the watchdog */
> +	writel(0, wdt->base + RZN1_WDT_RETRIGGER);
> +
> +	return 0;
> +}
> +
> +static int rzn1_wdt_start(struct watchdog_device *w)
> +{
> +	struct rzn1_watchdog *wdt = watchdog_get_drvdata(w);
> +	u32 val;
> +
> +	/*
> +	 * The hardware allows you to write to this reg only once.
> +	 * Since this includes the reload value, there is no way to change the
> +	 * timeout once started. Also note that the WDT clock is half the bus
> +	 * fabric clock rate, so if the bus fabric clock rate is changed after
> +	 * the WDT is started, the WDT interval will be wrong.
> +	 */
> +	val = RZN1_WDT_RETRIGGER_WDSI;
> +	val |= RZN1_WDT_RETRIGGER_ENABLE;
> +	val |= RZN1_WDT_RETRIGGER_PRESCALE;
> +	val |= compute_reload_value(w->max_hw_heartbeat_ms, wdt->clk_rate_khz);
> +	writel(val, wdt->base + RZN1_WDT_RETRIGGER);
> +
> +	return 0;
> +}
> +
> +static irqreturn_t rzn1_wdt_irq(int irq, void *_wdt)
> +{
> +	pr_crit("RZN1 Watchdog. Initiating system reboot\n");
> +	emergency_restart();
> +
> +	return IRQ_HANDLED;
> +}
> +
> +static struct watchdog_info rzn1_wdt_info = {
> +	.identity = "RZ/N1 Watchdog",
> +	.options = WDIOF_MAGICCLOSE | WDIOF_SETTIMEOUT | WDIOF_KEEPALIVEPING,
> +};
> +
> +static const struct watchdog_ops rzn1_wdt_ops = {
> +	.owner = THIS_MODULE,
> +	.start = rzn1_wdt_start,
> +	.ping = rzn1_wdt_ping,
> +};
> +
> +static void rzn1_wdt_clk_disable_unprepare(void *data)
> +{
> +	clk_disable_unprepare(data);
> +}
> +
> +static int rzn1_wdt_probe(struct platform_device *pdev)
> +{
> +	struct device *dev = &pdev->dev;
> +	struct rzn1_watchdog *wdt;
> +	struct device_node *np = dev->of_node;
> +	struct clk *clk;
> +	unsigned long clk_rate;
> +	int ret;
> +	int irq;
> +
> +	wdt = devm_kzalloc(dev, sizeof(*wdt), GFP_KERNEL);
> +	if (!wdt)
> +		return -ENOMEM;
> +
> +	wdt->base = devm_platform_ioremap_resource(pdev, 0);
> +	if (IS_ERR(wdt->base))
> +		return PTR_ERR(wdt->base);
> +
> +	irq = platform_get_irq(pdev, 0);
> +	if (irq < 0)
> +		return irq;
> +
> +	ret = devm_request_irq(dev, irq, rzn1_wdt_irq, 0,
> +			       np->name, wdt);
> +	if (ret) {
> +		dev_err(dev, "failed to request irq %d\n", irq);
> +		return ret;
> +	}
> +
> +	clk = devm_clk_get(dev, NULL);
> +	if (IS_ERR(clk)) {
> +		dev_err(dev, "failed to get the clock\n");
> +		return PTR_ERR(clk);
> +	}
> +
> +	ret = clk_prepare_enable(clk);
> +	if (ret) {
> +		dev_err(dev, "failed to prepare/enable the clock\n");
> +		return ret;
> +	}
> +
> +	ret = devm_add_action_or_reset(dev, rzn1_wdt_clk_disable_unprepare,
> +				       clk);
> +	if (ret)
> +		return ret;
> +
> +	clk_rate = clk_get_rate(clk);
> +	if (!clk_rate) {
> +		dev_err(dev, "failed to get the clock rate\n");
> +		return -EINVAL;
> +	}
> +
> +	wdt->clk_rate_khz = clk_rate / 1000;
> +	wdt->wdtdev.info = &rzn1_wdt_info,
> +	wdt->wdtdev.ops = &rzn1_wdt_ops,
> +	wdt->wdtdev.status = WATCHDOG_NOWAYOUT_INIT_STATUS,
> +	wdt->wdtdev.parent = dev;
> +	/*
> +	 * The period of the watchdog cannot be changed once set
> +	 * and is limited to a very short period.
> +	 * Configure it for a 1s period once and for all, and
> +	 * rely on the heart-beat provided by the watchdog core
> +	 * to make this usable by the user-space.
> +	 */
> +	wdt->wdtdev.max_hw_heartbeat_ms = max_heart_beat_ms(wdt->clk_rate_khz);
> +	if (wdt->wdtdev.max_hw_heartbeat_ms > 1000)
> +		wdt->wdtdev.max_hw_heartbeat_ms = 1000;
> +
> +	wdt->wdtdev.timeout = DEFAULT_TIMEOUT;
> +	ret = watchdog_init_timeout(&wdt->wdtdev, 0, dev);
> +	if (ret)
> +		return ret;
> +
> +	watchdog_set_drvdata(&wdt->wdtdev, wdt);
> +
> +	return devm_watchdog_register_device(dev, &wdt->wdtdev);
> +}
> +
> +
> +static const struct of_device_id rzn1_wdt_match[] = {
> +	{ .compatible = "renesas,rzn1-wdt" },
> +	{},
> +};
> +MODULE_DEVICE_TABLE(of, rzn1_wdt_match);
> +
> +static struct platform_driver rzn1_wdt_driver = {
> +	.probe		= rzn1_wdt_probe,
> +	.driver		= {
> +		.name		= KBUILD_MODNAME,
> +		.of_match_table	= rzn1_wdt_match,
> +	},
> +};
> +
> +module_platform_driver(rzn1_wdt_driver);
> +
> +MODULE_DESCRIPTION("Renesas RZ/N1 hardware watchdog");
> +MODULE_AUTHOR("Phil Edworthy <phil.edworthy@renesas.com>");
> +MODULE_LICENSE("GPL");