Date:   Thu, 26 Oct 2017 22:23:40 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Eric Long <eric.long@...eadtrum.com>,
        Wim Van Sebroeck <wim@...ana.be>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>
Cc:     baolin.wang@...aro.org, linux-watchdog@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/2] watchdog: Add Spreadtrum watchdog driver

On 10/26/2017 07:28 PM, Eric Long wrote:
> This patch adds the watchdog driver for Spreadtrum SC9860 platform.
> 
> Signed-off-by: Eric Long <eric.long@...eadtrum.com>
> ---
> Change since v2:
>   - Rename all the macors, add SPRD tag at the head of the macro names.
>   - Rename SPRD_WDT_CLK as SPRD_WTC_CNT_STEP.
>   - Remove the code which check timeout value at the wrong place.
>   - Add min/max timeout value limit.
>   - Remove set WDOG_HW_RUNNING status at sprd_wdt_enable().
>   - Add timeout/pretimeout judgment when set them.
>   - Support WATCHDOG_NOWAYOUT status.
> 
> Changes since v1:
>   - Use pretimeout instead of own implementation.
>   - Fix timeout loop when loading timeout values.
>   - use the infrastructure to read and set "timeout-sec" property.
>   - Add conditions when start or stop watchdog.
>   - Change the position of enabling watchdog.
>   - Other optimization.
> ---
>   drivers/watchdog/Kconfig    |   8 +
>   drivers/watchdog/Makefile   |   1 +
>   drivers/watchdog/sprd_wdt.c | 415 ++++++++++++++++++++++++++++++++++++++++++++
>   3 files changed, 424 insertions(+)
>   create mode 100644 drivers/watchdog/sprd_wdt.c
> 
> diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig
> index c722cbf..4a77e17 100644
> --- a/drivers/watchdog/Kconfig
> +++ b/drivers/watchdog/Kconfig
> @@ -787,6 +787,14 @@ config UNIPHIER_WATCHDOG
>   	  To compile this driver as a module, choose M here: the
>   	  module will be called uniphier_wdt.
>   
> +config SPRD_WATCHDOG
> +	tristate "Spreadtrum watchdog support"
> +	depends on ARCH_SPRD || COMPILE_TEST
> +	select WATCHDOG_CORE
> +	help
> +	  Say Y here to include support watchdog timer embedded
> +	  into the Spreadtrum system.

Maybe better "supported by" instead of "embedded into". Or at least
"embedded in".

> +
>   # AVR32 Architecture
>   
>   config AT32AP700X_WDT
> diff --git a/drivers/watchdog/Makefile b/drivers/watchdog/Makefile
> index 56adf9f..187cca2 100644
> --- a/drivers/watchdog/Makefile
> +++ b/drivers/watchdog/Makefile
> @@ -87,6 +87,7 @@ obj-$(CONFIG_ASPEED_WATCHDOG) += aspeed_wdt.o
>   obj-$(CONFIG_ZX2967_WATCHDOG) += zx2967_wdt.o
>   obj-$(CONFIG_STM32_WATCHDOG) += stm32_iwdg.o
>   obj-$(CONFIG_UNIPHIER_WATCHDOG) += uniphier_wdt.o
> +obj-$(CONFIG_SPRD_WATCHDOG) += sprd_wdt.o
>   
>   # AVR32 Architecture
>   obj-$(CONFIG_AT32AP700X_WDT) += at32ap700x_wdt.o
> diff --git a/drivers/watchdog/sprd_wdt.c b/drivers/watchdog/sprd_wdt.c
> new file mode 100644
> index 0000000..5fc3dde
> --- /dev/null
> +++ b/drivers/watchdog/sprd_wdt.c
> @@ -0,0 +1,415 @@
> +/*
> + * Spreadtrum watchdog driver
> + * Copyright (C) 2017 Spreadtrum - http://www.spreadtrum.com
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License
> + * version 2 as published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful, but
> + * WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> + * General Public License for more details.
> + */
> +
> +#include <linux/bitops.h>
> +#include <linux/clk.h>
> +#include <linux/err.h>
> +#include <linux/interrupt.h>
> +#include <linux/io.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/of_address.h>
> +#include <linux/platform_device.h>
> +#include <linux/watchdog.h>
> +
> +#define SPRD_WDT_LOAD_LOW		0x0
> +#define SPRD_WDT_LOAD_HIGH		0x4
> +#define SPRD_WDT_CTRL			0x8
> +#define SPRD_WDT_INT_CLR		0xc
> +#define SPRD_WDT_INT_RAW		0x10
> +#define SPRD_WDT_INT_MSK		0x14
> +#define SPRD_WDT_CNT_LOW		0x18
> +#define SPRD_WDT_CNT_HIGH		0x1c
> +#define SPRD_WDT_LOCK			0x20
> +#define SPRD_WDT_IRQ_LOAD_LOW		0x2c
> +#define SPRD_WDT_IRQ_LOAD_HIGH		0x30
> +
> +/* WDT_CTRL */
> +#define SPRD_WDT_INT_EN_BIT		BIT(0)
> +#define SPRD_WDT_CNT_EN_BIT		BIT(1)
> +#define SPRD_WDT_NEW_VER_EN		BIT(2)
> +#define SPRD_WDT_RST_EN_BIT		BIT(3)
> +
> +/* WDT_INT_CLR */
> +#define SPRD_WDT_INT_CLEAR_BIT		BIT(0)
> +#define SPRD_WDT_RST_CLEAR_BIT		BIT(3)
> +
> +/* WDT_INT_RAW */
> +#define SPRD_WDT_INT_RAW_BIT		BIT(0)
> +#define SPRD_WDT_RST_RAW_BIT		BIT(3)
> +#define SPRD_WDT_LD_BUSY_BIT		BIT(4)
> +
> +/* 1s equale to 32768 counter steps */

equal ?

> +#define SPRD_WDT_CNT_STEP		32768
> +
> +#define SPRD_WDT_UNLOCK_KEY		0xe551
> +#define SPRD_WDT_MIN_TIMROUT		3

TIMROUT ot TIMEOUT ?

> +#define SPRD_WDT_MAX_TIMEOUT		60

Is that really the maximum supported timeout ? Seems a bit low.
Shouldn't it be something like (U32_MAX / SPRD_WDT_CNT_STEP) ?

> +
> +#define SPRD_WDT_CNT_HIGH_VALUE		16

Maybe name it "SPRD_WDT_CNT_HIGH_SHIFT". It is not really a value,
it is a shift.

> +#define SPRD_WDT_LOW_VALUE_MASK		GENMASK(15, 0)
> +#define SPRD_WDT_CNT_VALUE_MAX		GENMASK(31, 0)

Does this mask serve a useful purpose ?

> +#define SPRD_WDT_LOAD_TIMEOUT		1000
> +
> +struct sprd_wdt {
> +	void __iomem *base;
> +	struct watchdog_device wdd;
> +	struct clk *enable;
> +	struct clk *rtc_enable;
> +	unsigned int irq;
> +};
> +
> +static inline struct sprd_wdt *to_sprd_wdt(struct watchdog_device *wdd)
> +{
> +	return container_of(wdd, struct sprd_wdt, wdd);
> +}
> +
> +static inline void sprd_wdt_lock(void __iomem *addr)
> +{
> +	writel_relaxed(0x0, addr + SPRD_WDT_LOCK);
> +}
> +
> +static inline void sprd_wdt_unlock(void __iomem *addr)
> +{
> +	writel_relaxed(SPRD_WDT_UNLOCK_KEY, addr + SPRD_WDT_LOCK);
> +}
> +
> +static inline bool sprd_wdt_is_running(struct sprd_wdt *wdt)
> +{
> +	u32 val;
> +
> +	val = readl_relaxed(wdt->base + SPRD_WDT_CTRL);
> +	return val & SPRD_WDT_NEW_VER_EN;
> +}
> +
> +static irqreturn_t sprd_wdt_isr(int irq, void *dev_id)
> +{
> +	struct sprd_wdt *wdt = (struct sprd_wdt *)dev_id;
> +
> +	sprd_wdt_unlock(wdt->base);
> +	writel_relaxed(SPRD_WDT_INT_CLEAR_BIT, wdt->base + SPRD_WDT_INT_CLR);
> +	sprd_wdt_lock(wdt->base);
> +	watchdog_notify_pretimeout(&wdt->wdd);
> +	return IRQ_HANDLED;
> +}
> +
> +static u32 sprd_wdt_get_cnt_value(struct sprd_wdt *wdt)
> +{
> +	u32 val;
> +
> +	val = readl_relaxed(wdt->base + SPRD_WDT_CNT_HIGH) <<
> +		SPRD_WDT_CNT_HIGH_VALUE;
> +	val |= readl_relaxed(wdt->base + SPRD_WDT_CNT_LOW) &
> +		SPRD_WDT_LOW_VALUE_MASK;
> +
> +	return val;
> +}
> +
> +static int sprd_wdt_load_value(struct sprd_wdt *wdt, u32 timeout,
> +			       u32 pretimeout)
> +{
> +	u32 val, delay_cnt = 0;
> +	u32 tmr_step = timeout * SPRD_WDT_CNT_STEP;
> +	u32 prtmr_step = pretimeout * SPRD_WDT_CNT_STEP;
> +
> +	sprd_wdt_unlock(wdt->base);
> +	writel_relaxed((tmr_step >> SPRD_WDT_CNT_HIGH_VALUE) &
> +		      SPRD_WDT_LOW_VALUE_MASK, wdt->base + SPRD_WDT_LOAD_HIGH);
> +	writel_relaxed((tmr_step & SPRD_WDT_LOW_VALUE_MASK),
> +		       wdt->base + SPRD_WDT_LOAD_LOW);
> +	writel_relaxed((prtmr_step >> SPRD_WDT_CNT_HIGH_VALUE) &
> +			SPRD_WDT_LOW_VALUE_MASK,
> +		       wdt->base + SPRD_WDT_IRQ_LOAD_HIGH);
> +	writel_relaxed(prtmr_step & SPRD_WDT_LOW_VALUE_MASK,
> +		       wdt->base + SPRD_WDT_IRQ_LOAD_LOW);
> +	sprd_wdt_lock(wdt->base);
> +
> +	/*
> +	 * Waiting the load value operation done,
> +	 * it needs two or three RTC clock cycles.
> +	 */
> +	do {
> +		val = readl_relaxed(wdt->base + SPRD_WDT_INT_RAW);
> +		if (!(val & SPRD_WDT_LD_BUSY_BIT))
> +			break;
> +
> +		cpu_relax();
> +	} while (delay_cnt++ < SPRD_WDT_LOAD_TIMEOUT);
> +
> +	if (delay_cnt >= SPRD_WDT_LOAD_TIMEOUT)
> +		return -EBUSY;
> +	return 0;
> +}
> +
> +static int sprd_wdt_enable(struct sprd_wdt *wdt)
> +{
> +	u32 val;
> +	int ret;
> +
> +	ret = clk_prepare_enable(wdt->enable);
> +	if (ret)
> +		return ret;
> +	ret = clk_prepare_enable(wdt->rtc_enable);
> +	if (ret)
> +		return ret;
> +
> +	sprd_wdt_unlock(wdt->base);
> +	val = readl_relaxed(wdt->base + SPRD_WDT_CTRL);
> +	val |= SPRD_WDT_NEW_VER_EN;
> +	writel_relaxed(val, wdt->base + SPRD_WDT_CTRL);
> +	sprd_wdt_lock(wdt->base);
> +	return 0;
> +}
> +
> +static void sprd_wdt_disable(struct sprd_wdt *wdt)
> +{
> +	sprd_wdt_unlock(wdt->base);
> +	writel_relaxed(0x0, wdt->base + SPRD_WDT_CTRL);
> +	sprd_wdt_lock(wdt->base);
> +
> +	clk_disable_unprepare(wdt->rtc_enable);
> +	clk_disable_unprepare(wdt->enable);
> +}
> +
> +static int sprd_wdt_start(struct watchdog_device *wdd)
> +{
> +	struct sprd_wdt *wdt = to_sprd_wdt(wdd);
> +	u32 val;
> +	int ret;
> +
> +	ret = sprd_wdt_load_value(wdt, wdd->timeout, wdd->pretimeout);
> +	if (ret)
> +		return ret;
> +
> +	sprd_wdt_unlock(wdt->base);
> +	val = readl_relaxed(wdt->base + SPRD_WDT_CTRL);
> +	val |= SPRD_WDT_CNT_EN_BIT | SPRD_WDT_INT_EN_BIT | SPRD_WDT_RST_EN_BIT;
> +	writel_relaxed(val, wdt->base + SPRD_WDT_CTRL);
> +	sprd_wdt_lock(wdt->base);
> +	set_bit(WDOG_HW_RUNNING, &wdd->status);
> +
> +	return 0;
> +}
> +
> +static int sprd_wdt_stop(struct watchdog_device *wdd)
> +{
> +	struct sprd_wdt *wdt = to_sprd_wdt(wdd);
> +	u32 val;
> +
> +	sprd_wdt_unlock(wdt->base);
> +	val = readl_relaxed(wdt->base + SPRD_WDT_CTRL);
> +	val &= ~(SPRD_WDT_CNT_EN_BIT | SPRD_WDT_RST_EN_BIT |
> +		SPRD_WDT_INT_EN_BIT);
> +	writel_relaxed(val, wdt->base + SPRD_WDT_CTRL);
> +	sprd_wdt_lock(wdt->base);
> +	return 0;
> +}
> +
> +static int sprd_wdt_set_timeout(struct watchdog_device *wdd,
> +				u32 timeout)
> +{
> +	struct sprd_wdt *wdt = to_sprd_wdt(wdd);
> +
> +	if (timeout == wdd->timeout)
> +		return 0;
> +
> +	wdd->timeout = timeout;
> +
> +	return sprd_wdt_load_value(wdt, timeout, wdd->pretimeout);
> +}
> +
> +static int sprd_wdt_set_pretimeout(struct watchdog_device *wdd,
> +				   u32 new_pretimeout)
> +{
> +	struct sprd_wdt *wdt = to_sprd_wdt(wdd);
> +
> +	if (new_pretimeout == wdd->pretimeout)
> +		return 0;

This is inconsistent. pretimeout == 0 is accepted until it is set
to a non-zero value once, then 0 is no longer accepted. pretimeout==0
should reflect "pretimeout disabled". If that is not possible you
need to set some non-0 default value in the probe function.

> +	if (new_pretimeout <= wdd->min_timeout)
> +		return -EINVAL;

Why is pretimeout == wdd->min_timeout invalid ?

> +
> +	wdd->pretimeout = new_pretimeout;
> +
> +	return sprd_wdt_load_value(wdt, wdd->timeout, new_pretimeout);
> +}
> +
> +static u32 sprd_wdt_get_timeleft(struct watchdog_device *wdd)
> +{
> +	struct sprd_wdt *wdt = to_sprd_wdt(wdd);
> +	u32 val;
> +
> +	val = sprd_wdt_get_cnt_value(wdt);
> +	val = val / SPRD_WDT_CNT_STEP;
> +
> +	return val;
> +}
> +
> +static const struct watchdog_ops sprd_wdt_ops = {
> +	.owner = THIS_MODULE,
> +	.start = sprd_wdt_start,
> +	.stop = sprd_wdt_stop,
> +	.set_timeout = sprd_wdt_set_timeout,
> +	.set_pretimeout = sprd_wdt_set_pretimeout,
> +	.get_timeleft = sprd_wdt_get_timeleft,

Just wondering - no heartbeat function ? Having to load the timer
values for each heartbeat is expensive.

> +};
> +
> +static const struct watchdog_info sprd_wdt_info = {
> +	.options = WDIOF_SETTIMEOUT |
> +		   WDIOF_PRETIMEOUT |
> +		   WDIOF_MAGICCLOSE |
> +		   WDIOF_KEEPALIVEPING,
> +	.identity = "Spreadtrum Watchdog Timer",
> +};
> +
> +static int sprd_wdt_probe(struct platform_device *pdev)
> +{
> +	struct resource *wdt_res;
> +	struct sprd_wdt *wdt;
> +	int ret;
> +
> +	wdt = devm_kzalloc(&pdev->dev, sizeof(*wdt), GFP_KERNEL);
> +	if (!wdt)
> +		return -ENOMEM;
> +
> +	wdt_res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> +	if (!wdt_res) {
> +		dev_err(&pdev->dev, "failed to memory resource\n");
> +		return -ENOMEM;
> +	}

Unnecessary error check and message. devm_ioremap_resource()
returns an error if res is NULL.

> +
> +	wdt->base = devm_ioremap_resource(&pdev->dev, wdt_res);
> +	if (IS_ERR(wdt->base))

Move the error message to here.

> +		return PTR_ERR(wdt->base);
> +
> +	wdt->enable = devm_clk_get(&pdev->dev, "enable");
> +	if (IS_ERR(wdt->enable)) {
> +		dev_err(&pdev->dev, "can't get the enable clock\n");
> +		return PTR_ERR(wdt->enable);
> +	}
> +
> +	wdt->rtc_enable = devm_clk_get(&pdev->dev, "rtc_enable");
> +	if (IS_ERR(wdt->rtc_enable)) {
> +		dev_err(&pdev->dev, "can't get the rtc enable clock\n");
> +		return PTR_ERR(wdt->rtc_enable);
> +	}
> +
> +	wdt->irq = platform_get_irq(pdev, 0);
> +	if (wdt->irq < 0) {
> +		dev_err(&pdev->dev, "failed to get IRQ resource\n");
> +		return wdt->irq;
> +	}
> +
> +	ret = devm_request_irq(&pdev->dev, wdt->irq, sprd_wdt_isr,
> +			       IRQF_NO_SUSPEND, "sprd-wdt", (void *)wdt);
> +	if (ret) {
> +		dev_err(&pdev->dev, "failed to register irq\n");
> +		return ret;
> +	}
> +
> +	wdt->wdd.info = &sprd_wdt_info;
> +	wdt->wdd.ops = &sprd_wdt_ops;
> +	wdt->wdd.parent = &pdev->dev;
> +	wdt->wdd.min_timeout = SPRD_WDT_MIN_TIMROUT;
> +	wdt->wdd.max_timeout = SPRD_WDT_MAX_TIMEOUT;
> +
You might want to set wdt->wdd.timeout to a default value.

> +	ret = sprd_wdt_enable(wdt);
> +	if (ret) {
> +		dev_err(&pdev->dev, "failed to enable wdt\n");
> +		return ret;
> +	}
> +

This needs a matching sprd_wdt_disable() call in the remove function.
Best way to handle this would be to add devm_add_action() here.

> +	watchdog_set_nowayout(&wdt->wdd, WATCHDOG_NOWAYOUT);
> +	watchdog_init_timeout(&wdt->wdd, 0, &pdev->dev);
> +
> +	ret = watchdog_register_device(&wdt->wdd);

Unfortunately this doesn't work. It leaves interrupts enabled
after the watchdog device is removed in sprd_wdt_remove(),
but the driver will be gone. I would suggest to use
devm_watchdog_register_device() and reorder calls to request
the interrupt after registering the watchdog device. Then you
can drop the remove function entirely.

> +	if (ret) {
> +		sprd_wdt_disable(wdt);
> +		dev_err(&pdev->dev, "failed to register watchdog\n");
> +		return ret;
> +	}
> +	platform_set_drvdata(pdev, wdt);
> +
> +	return 0;
> +}
> +
> +static int sprd_wdt_remove(struct platform_device *pdev)
> +{
> +	struct sprd_wdt *wdt = platform_get_drvdata(pdev);
> +
> +	watchdog_unregister_device(&wdt->wdd);
> +
> +	if (sprd_wdt_is_running(wdt))
> +		dev_crit(&pdev->dev, "Device removed: Expect reboot!\n");
> +	return 0;
> +}
> +
> +static int __maybe_unused sprd_wdt_pm_suspend(struct device *dev)
> +{
> +	struct watchdog_device *wdd = dev_get_drvdata(dev);
> +	struct sprd_wdt *wdt = dev_get_drvdata(dev);
> +
> +	if (watchdog_active(wdd)) {
> +		sprd_wdt_stop(&wdt->wdd);
> +		sprd_wdt_disable(wdt);

Are you sure you only want to disable the clocks if the watchdog was active ?
That seems to be a bit inconsistent.

> +	}
> +
> +	return 0;
> +}
> +
> +static int __maybe_unused sprd_wdt_pm_resume(struct device *dev)
> +{
> +	struct watchdog_device *wdd = dev_get_drvdata(dev);
> +	struct sprd_wdt *wdt = dev_get_drvdata(dev);
> +	int ret;
> +
> +	if (watchdog_active(wdd)) {
> +		ret = sprd_wdt_enable(wdt);
> +		if (ret)
> +			return ret;
> +		ret = sprd_wdt_start(&wdt->wdd);
> +		if (ret) {
> +			sprd_wdt_disable(wdt);
> +			return ret;
> +		}

This can leave the system in an inconsistent state. Sometimes the wdt may be
disabled, sometimes not.

> +	}
> +
> +	return 0;
> +}
> +
> +static const struct dev_pm_ops sprd_wdt_pm_ops = {
> +	SET_SYSTEM_SLEEP_PM_OPS(sprd_wdt_pm_suspend,
> +				sprd_wdt_pm_resume)
> +};
> +
> +static const struct of_device_id sprd_wdt_match_table[] = {
> +	{ .compatible = "sprd,sp9860-wdt", },
> +	{},
> +};
> +MODULE_DEVICE_TABLE(of, sprd_wdt_match_table);
> +
> +static struct platform_driver sprd_watchdog_driver = {
> +	.probe	= sprd_wdt_probe,
> +	.remove	= sprd_wdt_remove,
> +	.driver	= {
> +		.name = "sprd-wdt",
> +		.of_match_table = sprd_wdt_match_table,
> +		.pm = &sprd_wdt_pm_ops,
> +	},
> +};
> +module_platform_driver(sprd_watchdog_driver);
> +
> +MODULE_AUTHOR("Eric Long <eric.long@...eadtrum.com>");
> +MODULE_DESCRIPTION("Spreadtrum Watchdog Timer Controller Driver");
> +MODULE_LICENSE("GPL v2");
> 

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