Date:   Tue, 23 Jun 2020 06:20:30 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Johnson CH Chen (陳昭勳) 
        <JohnsonCH.Chen@...a.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:     "linux-rtc@...r.kernel.org" <linux-rtc@...r.kernel.org>,
        "linux-watchdog@...r.kernel.org" <linux-watchdog@...r.kernel.org>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Lee Jones <lee.jones@...aro.org>
Subject: Re: [PATCH 3/3] watchdog: ds1374_wdt: Introduce Dallas/Maxim DS1374
 Watchdog driver

On 6/22/20 11:28 PM, Johnson CH Chen (陳昭勳) wrote:
> Hi,
> 
> Thanks for your good detailed suggestions!
> 

Other feedback suggests to convert the driver to use
the watchdog core in the rtc code. I would suggest to follow
that suggestion.

>>> + * It would be more efficient to use i2c msgs/i2c_transfer directly
>>> +but, as
>>> + * recommened in .../Documentation/i2c/writing-clients section
>>> + * "Sending and receiving", using SMBus level communication is preferred.
>>> + */
>>> +
>>> +#include <linux/kernel.h>
>>> +#include <linux/device.h>
>>> +#include <linux/module.h>
>>> +#include <linux/ioctl.h>
>>> +#include <linux/reboot.h>
>>> +#include <linux/watchdog.h>
>>> +#include <linux/workqueue.h>
>>> +#include <linux/platform_device.h>
>>> +#include <linux/i2c.h>
>>> +#include <linux/uaccess.h>
>>
>> Alphabetic order please.
>>
>>> +
>>> +#define DEVNAME                 "ds1374_wdt"
>>> +
>>> +#define DS1374_REG_WDALM0	0x04 /* Watchdog/Alarm */
>>> +#define DS1374_REG_WDALM1	0x05
>>> +#define DS1374_REG_WDALM2	0x06
>>> +#define DS1374_REG_CR		0x07 /* Control */
>>> +#define DS1374_REG_CR_AIE	0x01 /* Alarm Int. Enable */
>>> +#define DS1374_REG_CR_WDSTR     0x08 /* 1=INT, 0=RST */
>>> +#define DS1374_REG_CR_WDALM	0x20 /* 1=Watchdog, 0=Alarm */
>>> +#define DS1374_REG_CR_WACE	0x40 /* WD/Alarm counter enable */
>>> +
>>> +/* Default margin */
>>> +#define WD_TIMO                 131762
>>> +#define TIMER_MARGIN_MIN	4096 /* 1s */
>>> +#define TIMER_MARGIN_MAX	(60*60*24*4096) /* one day */
>>> +
>>> +static int wdt_margin = WD_TIMO;
>>
>> Sjould not be pre-initialized. Also, 131762 isn't 32 seconds, it is 131,762
>> seconds.
>>
> 
> 131762 is 32 seconds actually because watchdog counter increases per 
> 1/4096 seconds for DS1374. If DS1374_REG_CR_WDALM is set to 0 (alarm), 
> alarm counter will increase per 1 second.
> 

The watchdog core keeps timeouts in seconds. For the watchdog core,
131762 is 131,762 seconds. Your code assumes that the watchdog core
does not care about / need to scale, which is wrong. Besides,
MODULE_PARM_DESC below clearly states "Watchdog timeout _in seconds_"
(emphasis added).

>>> +module_param(wdt_margin, int, 0);
>>> +MODULE_PARM_DESC(wdt_margin, "Watchdog timeout in seconds (default
>>> +32s)");
>>> +
>>
>> As a new driver, it would be better to just use the customary "timeout".
>>
>>> +static bool nowayout = WATCHDOG_NOWAYOUT; module_param(nowayout,
>>> +bool, 0); MODULE_PARM_DESC(nowayout, "Watchdog cannot be stopped
>> once
>>> +started default ="
>>> +		__MODULE_STRING(WATCHDOG_NOWAYOUT) ")");
>>> +
>>> +struct ds1374_wdt {
>>> +	struct i2c_client *client;
>>> +	struct watchdog_device *wdt;
>>> +	struct work_struct work;
>>
>> Not used.
>>
>>> +
>>> +	/* The mutex protects alarm operations, and prevents a race
>>> +	 * between the enable_irq() in the workqueue and the free_irq()
>>> +	 * in the remove function.
>>> +	 */
>>
>> There is no workqueue here, and the remove function is not needed.
>>
>>> +	struct mutex mutex;
>>> +};
>>> +
>>> +static const struct watchdog_info ds1374_wdt_info = {
>>> +	.identity       = DEVNAME,
>>> +	.options        = WDIOF_SETTIMEOUT | WDIOF_KEEPALIVEPING |
>>> +						WDIOF_MAGICCLOSE,
>>> +};
>>> +
>>> +static struct watchdog_device ds1374_wdd;
>>> +
>> Move declaration please.
>>
>>> +static int ds1374_wdt_settimeout(struct watchdog_device *wdt,
>>> +					unsigned int timeout)
>>> +{
>>
>> How is this synchronized against accesses by the RTC driver ?
>>
> By original design in rtc-ds1374.c, it seems no synchronized problem between 
> rtc and watchdog, but I think we can add mutex lock to deal with it.
> 
The mutex is used there where needed.

>>> +	int ret = -ENOIOCTLCMD;
>>
>> Not an appropriate error code here.
>>
>>> +	u8 buf[4];
>>> +	int cr, i;
>>> +	struct ds1374_wdt *drv_data = watchdog_get_drvdata(wdt);
>>> +
>>> +	ret = cr = i2c_smbus_read_byte_data(drv_data->client, DS1374_REG_CR);
>>> +	if (ret < 0)
>>> +		goto out;
>>
>> "goto out;" is unnecessary. Just return the error. Same everywhere else below.
>>
>>> +
>>> +	/* Disable any existing watchdog/alarm before setting the new one */
>>> +	cr &= ~DS1374_REG_CR_WACE;
>>> +
>>> +	ret = i2c_smbus_write_byte_data(drv_data->client, DS1374_REG_CR, cr);
>>> +	if (ret < 0)
>>> +		goto out;
>>> +
>>> +	/* Set new watchdog time */
>>> +	for (i = 0; i < 3; i++) {
>>> +		buf[i] = timeout & 0xff;
>>> +		timeout >>= 8;
>>> +	}
>>
>> The value passed to this function from the watchdog core is the timeout in
>> seconds. I don't see a conversion to internal values here.
>>
> 
> For original design in rtc-ds1374.c, ds1374_wdt_settimeout () will call 
> ds1374_write_rtc() to write hardware register. To separate watchdog and rtc 
> functions, expand code from ds1374_write_rtc() here, and final buf[] values 
> will be written into hardware register for DS1374.
> 

ds1374_wdt_settimeout() is an API function, It gets timeouts from the watchdog
core in seconds. Those timeouts have to be converted to chip internal values
in this function.

>>> +
>>> +	ret = i2c_smbus_write_i2c_block_data(drv_data->client,
>>> +						DS1374_REG_WDALM0, 3, buf);
>>> +	if (ret) {
>>> +		pr_info("couldn't set new watchdog time\n");
>>> +		goto out;
>>> +	}
>>
>>> +
>>> +	/* Enable watchdog timer */
>>> +	cr |= DS1374_REG_CR_WACE | DS1374_REG_CR_WDALM;
>>> +	cr &= ~DS1374_REG_CR_WDSTR;/* for RST PIN */
>>> +	cr &= ~DS1374_REG_CR_AIE;
>>> +
>>> +	ret = i2c_smbus_write_byte_data(drv_data->client, DS1374_REG_CR, cr);
>>> +	if (ret < 0)
>>> +		goto out;
>>> +
>>> +	return 0;
>>
>> Pointless. Just return ret.
>>
>> Also, this function needs to store the new timeout in struct watchdog_device.
>>
>>> +out:
>>> +	return ret;
>>> +}
>>> +
>>> +
>>> +/*
>>> + * Read WD/Alarm counter to reload the watchdog timer. (ie, pat the
>>> +watchdog)  */ static int ds1374_wdt_ping(struct watchdog_device *wdt)
>>> +{
>>> +	struct ds1374_wdt *drv_data = watchdog_get_drvdata(wdt);
>>> +	int ret;
>>> +	u8 buf[4];
>>> +
>>> +	ret = i2c_smbus_read_i2c_block_data(drv_data->client,
>>> +						DS1374_REG_WDALM0, 3, buf);
>>> +
>>> +	if (ret < 0 || ret < 3)
>>> +		pr_info("WD TICK FAIL!!!!!!!!!! %i\n", ret);
>>> +
>>
>> This is not an info message, this is an error. Besides, it is just noise.
>> Just return the error and drop the message.
>>
>>> +	return ret;
>>> +}
>>> +
>>> +static int ds1374_wdt_start(struct watchdog_device *wdt) {
>>> +	int ret;
>>> +
>>> +	ret = ds1374_wdt_settimeout(wdt, wdt_margin);
>>
>> This is wrong. The timeout may have been updated by userspace.
>> It is inappropriate to change it back to the default here.
>>
> Thanks, I will keep in mind.
> 
>>> +	if (ret)
>>> +		return ret;
>>> +
>>> +	ds1374_wdt_ping(wdt);
>>
>> Please do not ignore errors.
>>
>>> +
>>> +	return 0;
>>> +}
>>> +
>>> +static int ds1374_wdt_stop(struct watchdog_device *wdt) {
>>> +	struct ds1374_wdt *drv_data = watchdog_get_drvdata(wdt);
>>> +	int cr;
>>> +
>>> +	if (nowayout)
>>> +		return 0;
>>
>> Not needed.
>>
> Thanks!, it has been implemented in watchdog_stop().
> 
>>> +
>>> +	cr = i2c_smbus_read_byte_data(drv_data->client, DS1374_REG_CR);
>>> +	/* Disable watchdog timer */
>>> +	cr &= ~DS1374_REG_CR_WACE;
>>> +
>>> +	return i2c_smbus_write_byte_data(drv_data->client, DS1374_REG_CR,
>>> +cr); }
>>> +
>>> +/*
>>> + * Handle commands from user-space.
>>> + */
>>> +static long ds1374_wdt_ioctl(struct watchdog_device *wdt, unsigned int
>> cmd,
>>> +				unsigned long arg)
>>
>> The whole point of using the watchdog subsystem is to not need a local ioctl
>> function - and most definitely not one that duplicates watchdog core
>> functionality.
>>
>>> +{
>>> +	int new_margin, options;
>>> +
>>> +	switch (cmd) {
>>> +	case WDIOC_GETSUPPORT:
>>> +		return copy_to_user((struct watchdog_info __user *)arg,
>>> +		&ds1374_wdt_info, sizeof(ds1374_wdt_info)) ? -EFAULT : 0;
>>> +
>>> +	case WDIOC_GETSTATUS:
>>> +	case WDIOC_GETBOOTSTATUS:
>>> +		return put_user(0, (int __user *)arg);
>>> +	case WDIOC_KEEPALIVE:
>>> +		ds1374_wdt_ping(wdt);
>>> +		return 0;
>>> +	case WDIOC_SETTIMEOUT:
>>> +		if (get_user(new_margin, (int __user *)arg))
>>> +			return -EFAULT;
>>> +
>>> +		/* the hardware's tick rate is 4096 Hz, so
>>> +		 * the counter value needs to be scaled accordingly
>>> +		 */
>>> +		new_margin <<= 12;
>>> +		if (new_margin < 1 || new_margin > 16777216)
>>> +			return -EINVAL;
>>> +
>>> +		wdt_margin = new_margin;
>>> +		ds1374_wdt_settimeout(wdt, new_margin);
>>
>> Is the idea here to bypass the watchdog subsystem's notion of keeping the
>> timeout in seconds ? If so, that would be wrong and unacceptable.
>>
> It seems take care about 4096Hz for original design in rtc-ds1374.c. I think we
> can just use ioctl() which watchdog core provides and input margin time
> appropriately.
> 
> 
>>> +		ds1374_wdt_ping(wdt);
>>> +		fallthrough;
>>> +	case WDIOC_GETTIMEOUT:
>>> +		/* when returning ... inverse is true */
>>> +		return put_user((wdt_margin >> 12), (int __user *)arg);
>>> +	case WDIOC_SETOPTIONS:
>>> +		if (copy_from_user(&options, (int __user *)arg, sizeof(int)))
>>> +			return -EFAULT;
>>> +
>>> +		if (options & WDIOS_DISABLECARD) {
>>> +			pr_info("disable watchdog\n");
>>> +			ds1374_wdt_stop(wdt);
>>> +			return 0;
>>> +		}
>>> +
>>> +		if (options & WDIOS_ENABLECARD) {
>>> +			pr_info("enable watchdog\n");
>>> +			ds1374_wdt_settimeout(wdt, wdt_margin);
>>> +			ds1374_wdt_ping(wdt);
>>> +			return 0;
>>> +		}
>>> +		return -EINVAL;
>>> +	}
>>> +	return -ENOTTY;
>>> +}
>>> +
>>> +static int ds1374_wdt_notify_sys(struct notifier_block *this,
>>> +			unsigned long code, void *unused)
>>> +{
>>> +	if (code == SYS_DOWN || code == SYS_HALT)
>>> +		/* Disable Watchdog */
>>> +		ds1374_wdt_stop(&ds1374_wdd);
>>> +	return NOTIFY_DONE;
>>> +}
>>> +
>> Not needed - see below.
>>
>>> +static struct notifier_block ds1374_wdt_notifier = {
>>> +	.notifier_call = ds1374_wdt_notify_sys, };
>>> +
>>> +static int ds1374_wdt_probe(struct platform_device *pdev) {
>>> +	struct ds1374_wdt *drv_data;
>>> +	struct i2c_client *client = to_i2c_client(pdev->dev.parent);
>>> +	int ret;
>>> +
>>> +	drv_data = devm_kzalloc(&pdev->dev, sizeof(struct ds1374_wdt),
>>> +				GFP_KERNEL);
>>> +	if (!drv_data)
>>> +		return -ENOMEM;
>>> +
>>> +	drv_data->wdt = &ds1374_wdd;
>>> +	drv_data->client = client;
>>> +	mutex_init(&drv_data->mutex);
>>> +
>>> +	watchdog_init_timeout(drv_data->wdt, wdt_margin, &pdev->dev);
>>> +	watchdog_set_nowayout(drv_data->wdt, nowayout);
>>> +
>>> +	watchdog_set_drvdata(drv_data->wdt, drv_data);
>>> +	platform_set_drvdata(pdev, drv_data);
>>> +
>>> +	ret = watchdog_register_device(drv_data->wdt);
>>
>> Use devm_watchdog_register_device()
>>
>>> +	if (ret) {
>>> +		dev_err(&pdev->dev, "failed to register Watchdog device\n");
>>> +		return ret;
>>> +	}
>>> +
>>> +	ret = register_reboot_notifier(&ds1374_wdt_notifier);
>>
>> Call watchdog_stop_on_reboot() before calling watchdog_register_device()
>> instead.
>>
>>> +	if (ret) {
>>> +		watchdog_unregister_device(drv_data->wdt);
>>> +		return ret;
>>> +	}
>>> +
>>> +	ds1374_wdt_settimeout(drv_data->wdt, wdt_margin);
>>
>> Unnecessary here; called from start function.
>>
>>> +	dev_info(&pdev->dev, "Dallas/Maxim DS1374 watchdog device
>>> +enabled\n");
>>> +
>>> +	return 0;
>>> +}
>>> +
>>> +static int ds1374_wdt_remove(struct platform_device *pdev) {
>>> +	struct ds1374_wdt *drv_data = platform_get_drvdata(pdev);
>>> +
>>> +	dev_warn(&pdev->dev, "Unregister DS1374 watchdog device\n");
>>> +	watchdog_unregister_device(drv_data->wdt);
>>> +	unregister_reboot_notifier(&ds1374_wdt_notifier);
>>> +
>>
>> Call watchdog_stop_on_unregister() before calling
>> watchdog_register_device().
>>
>>> +	return 0;
>>> +}
>>> +
>>> +static void ds1374_wdt_shutdown(struct platform_device *pdev) {
>>> +	struct ds1374_wdt *drv_data = platform_get_drvdata(pdev);
>>> +
>>> +	mutex_lock(&drv_data->mutex);
>>> +	ds1374_wdt_stop(drv_data->wdt);
>>> +	mutex_unlock(&drv_data->mutex);
>>
>> Unnecessary and pointless.
>>
>>> +}
>>> +
>>> +static const struct watchdog_ops ds1374_wdt_fops = {
>>> +	.owner          = THIS_MODULE,
>>> +	.start          = ds1374_wdt_start,
>>> +	.stop           = ds1374_wdt_stop,
>>> +	.ping           = ds1374_wdt_ping,
>>> +	.set_timeout    = ds1374_wdt_settimeout,
>>> +	.ioctl          = ds1374_wdt_ioctl,
>>> +};
>>> +
>>> +static struct watchdog_device ds1374_wdd = {
>>> +	.info           = &ds1374_wdt_info,
>>> +	.ops            = &ds1374_wdt_fops,
>>> +	.min_timeout    = TIMER_MARGIN_MIN,
>>> +	.max_timeout    = TIMER_MARGIN_MAX,
>>
>> .timeout should be set here.
>>
>> Also, there can (at least in theory) be more than one ds1374 in the system. The
>> code does not support this case. ds1374_wdd should be moved into struct
>> ds1374_wdt.
>>
> Thanks for good suggestion.
>>> +};
>>> +
>>> +static struct platform_driver ds1374_wdt = {
>>> +	.driver         = {
>>> +		.owner  = THIS_MODULE,
>>> +		.name   = DEVNAME,
>>> +	},
>>> +	.probe          = ds1374_wdt_probe,
>>> +	.remove         = ds1374_wdt_remove,
>>> +	.shutdown       = ds1374_wdt_shutdown,
>>> +};
>>> +
>>> +module_platform_driver(ds1374_wdt);
>>> +
>>> +MODULE_AUTHOR("Johnson Chen <johnsonch.chen@...a.com>");
>>> +MODULE_DESCRIPTION("Dallas/Maxim DS1374 Watchdog Driver");
>>> +MODULE_LICENSE("GPL"); MODULE_ALIAS("Platform:ds1374_wdt");
>>>
> 
> Best regards,
> Johnson
> 

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