Date:   Wed, 25 Oct 2017 04:13:42 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Wim Van Sebroeck <wim@...ana.be>, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>, baolin.wang@...aro.org,
        linux-watchdog@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [v2,2/2] watchdog: Add Spreadtrum watchdog driver

On 10/25/2017 03:29 AM, Eric Long wrote:
> Hi Guenter,
> 
> Sorry for late reply, and thanks for your detail comments.
> 
> On Sun, Oct 22, 2017 at 09:07:29AM -0700, Guenter Roeck wrote:
>> On Tue, Sep 12, 2017 at 07:40:09PM +0800, Eric Long wrote:
>>> This patch adds the watchdog driver for Spreadtrum SC9860 platform.
>>>
>>> Signed-off-by: Eric Long <eric.long@...eadtrum.com>
>>> ---
>>> 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 | 384 ++++++++++++++++++++++++++++++++++++++++++++
>>>   3 files changed, 393 insertions(+)
>>>   create mode 100644 drivers/watchdog/sprd_wdt.c
>>>
>>> diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig
>>> index c722cbf..ea07718 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
>>> +	select WATCHDOG_CORE
>>> +	help
>>> +	  Say Y here to include support watchdog timer embedded
>>> +	  into the Spreadtrum system.
>>> +
>>>   # 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..dedbca6fd
>>> --- /dev/null
>>> +++ b/drivers/watchdog/sprd_wdt.c
>>> @@ -0,0 +1,384 @@
>>> +/*
>>> + * 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/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 WDT_LOAD_LOW		0x0
>>> +#define WDT_LOAD_HIGH		0x4
>>> +#define WDT_CTRL		0x8
>>> +#define WDT_INT_CLR		0xc
>>> +#define WDT_INT_RAW		0x10
>>> +#define WDT_INT_MSK		0x14
>>> +#define WDT_CNT_LOW		0x18
>>> +#define WDT_CNT_HIGH		0x1c
>>> +#define WDT_LOCK		0x20
>>> +#define WDT_IRQ_LOAD_LOW	0x2c
>>> +#define WDT_IRQ_LOAD_HIGH	0x30
>>> +
>>> +/* WDT_CTRL */
>>> +#define WDT_INT_EN_BIT		BIT(0)
>>> +#define WDT_CNT_EN_BIT		BIT(1)
>>> +#define WDT_NEW_VER_EN		BIT(2)
>>> +#define WDT_RST_EN_BIT		BIT(3)
>>> +
>>> +/* WDT_INT_CLR */
>>> +#define WDT_INT_CLEAR_BIT	BIT(0)
>>> +#define WDT_RST_CLEAR_BIT	BIT(3)
>>> +
>> Requires include of bitops.h.
> 
> OK, I will fix it.
> 
>>> +/* WDT_INT_RAW */
>>> +#define WDT_INT_RAW_BIT		BIT(0)
>>> +#define WDT_RST_RAW_BIT		BIT(3)
>>> +#define WDT_LD_BUSY_BIT		BIT(4)
>>> +
>>> +#define WDT_CLK			32768
>>
>> Would it make sense to use clk_get_rate() instead ?
> 
> This wdt works at 153.6MHz, but its count step is 32768,
> so it cannot get the count step value by clk_get_rate().
>   
Please add a comment, and maybe rename the define to avoid the assumption
that it is related to the clock rate.

>>> +#define WDT_UNLOCK_KEY		0xe551
>>> +#define WDT_DEFAULT_PRETMROUT	3
>>> +
>>> +#define WDT_CNT_VALUE_SIZE	16
>>> +#define WDT_CNT_VALUE_MASK	GENMASK(15, 0)
>>> +#define WDT_LOAD_TIMEOUT_NUM	10000
>>> +
>>> +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 + WDT_LOCK);
>>> +}
>>> +
>>> +static inline void sprd_wdt_unlock(void __iomem *addr)
>>> +{
>>> +	writel_relaxed(WDT_UNLOCK_KEY, addr + WDT_LOCK);
>>> +}
>>> +
>>> +static inline bool sprd_wdt_is_running(struct sprd_wdt *wdt)
>>> +{
>>> +	u32 val;
>>> +
>>> +	val = readl_relaxed(wdt->base + WDT_CTRL);
>>> +	return val & 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(WDT_INT_CLEAR_BIT, wdt->base + 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 + WDT_CNT_HIGH) << WDT_CNT_VALUE_SIZE;
>>> +	val |= readl_relaxed(wdt->base + WDT_CNT_LOW) & WDT_CNT_VALUE_MASK;
>>> +
>>> +	return val;
>>> +}
>>> +
>>> +static int sprd_wdt_load_value(struct sprd_wdt *wdt, u32 timeout,
>>> +			       u32 pretimeout)
>>> +{
>>> +	u32 val, cnt = 0;
>>> +
>>> +	if (timeout < pretimeout)
>>> +		return -EINVAL;
>>> +
>>
>> This is the wrong place to check if the timeout is valid.
>> The core should know about limits and perform the checks.
> 
> OK, I will fix it.
>   
>>> +	if (!pretimeout)
>>> +		pretimeout = WDT_DEFAULT_PRETMROUT;
>>> +
>>
>> If pretimeout was 0 and timeout < 3, this will accept the timeout. If the
>> pretimeout is mandatory, it should be enforced, and the minimum timeout
>> should be larger than the miniumum pretimeout.
> 
> OK, I will add min/max timeout at probe function.
> 
>>> +	sprd_wdt_unlock(wdt->base);
>>> +	writel_relaxed(((timeout * WDT_CLK) >> WDT_CNT_VALUE_SIZE) &
>>> +		       WDT_CNT_VALUE_MASK, wdt->base + WDT_LOAD_HIGH);
>>
>> This can overflow. The maximum timeout must be <= 0xffffffff / WDT_CLK.
> 
> Yes, you are right, I will fix it, and the timeout value will be limited
> by min/max timeout, so there is no need to judge this timeout value after
> I add min/max timeout at probe function.
>   
>>> +	writel_relaxed(((timeout * WDT_CLK) & WDT_CNT_VALUE_MASK),
>>> +		       wdt->base + WDT_LOAD_LOW);
>>> +	writel_relaxed(((pretimeout * WDT_CLK) >> WDT_CNT_VALUE_SIZE) &
>>> +			WDT_CNT_VALUE_MASK, wdt->base + WDT_IRQ_LOAD_HIGH);
>>
>> Same for pretimeout.
>>
>>> +	writel_relaxed((pretimeout * WDT_CLK) & WDT_CNT_VALUE_MASK,
>>> +		       wdt->base + 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 + WDT_INT_RAW);
>>> +		if (!(val & WDT_LD_BUSY_BIT))
>>> +			break;
>>> +
>>> +		cpu_relax();
>>> +	} while (cnt++ < WDT_LOAD_TIMEOUT_NUM);
>>> +
>>> +	if (cnt >= WDT_LOAD_TIMEOUT_NUM)
>>> +		return -EBUSY;
>>> +	return 0;
>>> +}
>>> +
>>> +static void sprd_wdt_enable(struct sprd_wdt *wdt)
>>> +{
>>> +	u32 val;
>>> +
>>> +	clk_prepare_enable(wdt->enable);
>>> +	clk_prepare_enable(wdt->rtc_enable);
>>
>> Both functions can fail.
> 
> OK, I will fix it.
>   
>>> +
>>> +	sprd_wdt_unlock(wdt->base);
>>> +	val = readl_relaxed(wdt->base + WDT_CTRL);
>>> +	val |= WDT_NEW_VER_EN;
>>> +	writel_relaxed(val, wdt->base + WDT_CTRL);
>>> +	sprd_wdt_lock(wdt->base);
>>> +	set_bit(WDOG_HW_RUNNING, &wdt->wdd.status);
>>
>> Why ? The watchdog isn't started here.
> 
> OK, I will delete it.
> 
>>> +}
>>> +
>>> +static void sprd_wdt_disable(struct sprd_wdt *wdt)
>>> +{
>>> +	sprd_wdt_unlock(wdt->base);
>>> +	writel_relaxed(0x0, wdt->base + WDT_CTRL);
>>> +	sprd_wdt_lock(wdt->base);
>>> +
>>> +	clk_disable(wdt->enable);
>>> +	clk_disable(wdt->rtc_enable);
>>
>> clk_prepare_enable but no matching clk_disable_unprepare ?
> 
> Yes, thanks, you are right, it should use clk_disable_unprepare to instead.
> 
>>> +}
>>> +
>>> +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 + WDT_CTRL);
>>> +	val |= WDT_CNT_EN_BIT | WDT_INT_EN_BIT | WDT_RST_EN_BIT;
>>> +	writel_relaxed(val, wdt->base + 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 + WDT_CTRL);
>>> +	val &= ~(WDT_CNT_EN_BIT | WDT_RST_EN_BIT | WDT_INT_EN_BIT);
>>> +	writel_relaxed(val, wdt->base + 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);
>>> +
>>> +	wdd->timeout = timeout;
>>> +
>>> +	return sprd_wdt_load_value(wdt, timeout, wdd->pretimeout);
>>
>> Even on error, this accepts the new (bad) timeout.
> 
> OK, I should add judgment api here.
>   
No, you should provide limits to the core and let the core handle it.

>>> +}
>>> +
>>> +static int sprd_wdt_set_pretimeout(struct watchdog_device *wdd,
>>> +				   u32 new_pretimeout)
>>> +{
>>> +	struct sprd_wdt *wdt = to_sprd_wdt(wdd);
>>> +
>>> +	wdd->pretimeout = new_pretimeout;
>>> +
>>> +	return sprd_wdt_load_value(wdt, wdd->timeout, new_pretimeout);
>>
>> Even on error, this accepts the new (bad) pretimeout.
> 
> OK, I should add judgment api here.
>   
>>> +}
>>> +
>>> +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 / WDT_CLK;
>>> +
>>> +	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,
>>> +};
>>> +
>>> +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;
>>> +	}
>>> +
>>> +	wdt->base = devm_ioremap_nocache(&pdev->dev, wdt_res->start,
>>> +					 resource_size(wdt_res));
>>
>> Consider using devm_ioremap_resource().
> 
> Yes, thanks, devm_ioremap_resource() will be better.
>   
>>> +	if (!wdt->base)
>>> +		return -ENOMEM;
>>> +
>>> +	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;
>>> +
>>
>> This should also set limits for min/max to let the core validate ranges.
>> If the minimum pretimeout is 3 seconds, the lower limit for timeout should
>> be set accordingly.
> 
> Yes, you are right, I should add min/max timeout to limit the validate ranges, thanks.
>   
>>> +	sprd_wdt_enable(wdt);
>>> +
>>> +	watchdog_init_timeout(&wdt->wdd, 0, &pdev->dev);
>>> +
>>> +	ret = watchdog_register_device(&wdt->wdd);
>>> +	if (ret) {
>>> +		dev_err(&pdev->dev, "failed to register watchdog\n");
>>
>> No wdt disable on error ?
> 
> Yes, it should call sprd_wdt_disable().
> 
>>> +		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);
>>> +
>>> +	if (sprd_wdt_is_running(wdt)) {
>>> +		sprd_wdt_stop(&wdt->wdd);
>>> +		sprd_wdt_disable(wdt);
>>> +	}
>>
>> I assume you understand that this defeats NOWAYOUT.
> 
> In my understand, if NOWAYOUT is set, this watchdog cannot be stopped,
> but we hope the watchdog can be stopped when someone want to debug the kernel.
> 

I would suggest that maybe NOWAYOUT should not be enabled in that case.

Anyway, looks like the driver doesn't support NOWAYOUT anyway (why ?).
So what this defeats is MAGICCLOSE, and I still don't understand the logic
behind it. If you don't want to support it, fine, then just don't set the flag,
and the core will stop the watchdog for you.

Please add a short note to the driver explaining why you don't want those
flags to be supported, to prevent others from adding it later.

Thanks,
Guenter

>>> +	watchdog_unregister_device(&wdt->wdd);
>>> +
>>> +	return 0;
>>> +}
>>> +
>>> +static int __maybe_unused sprd_wdt_pm_suspend(struct device *dev)
>>> +{
>>> +	struct sprd_wdt *wdt = dev_get_drvdata(dev);
>>> +
>>> +	if (sprd_wdt_is_running(wdt)) {
>>
>> if (watchdog_active()) should work here.
> 
> Yes, you are right, I will fix it, thanks.
>   
>>> +		sprd_wdt_stop(&wdt->wdd);
>>> +		sprd_wdt_disable(wdt);
>>> +	}
>>> +
>>> +	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);
>>> +
>>> +	if (watchdog_active(wdd) && !sprd_wdt_is_running(wdt)) {
>>
>> sprd_wdt_is_running() should not be needed.
> 
> OK, I will fix it, thanks.
> 
>>> +		sprd_wdt_enable(wdt);
>>> +		sprd_wdt_start(&wdt->wdd);
>>> +	}
>>> +
>>> +	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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