Date:	Wed, 02 Oct 2013 21:27:03 +0200
From:	boris brezillon <b.brezillon@...rkiz.com>
To:	Guenter Roeck <linux@...ck-us.net>
CC:	Wim Van Sebroeck <wim@...ana.be>,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	Jean-Christophe PLAGNIOL-VILLARD <plagnioj@...osoft.com>,
	Ludovic Desroches <ludovic.desroches@...el.com>,
	Yang Wenyou <Wenyou.Yang@...el.com>,
	linux-watchdog@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [v2,1/4] watchdog: at91sam9_wdt: better watchdog support

Hello Guenter,

Thanks for reviewing this patch.

On 02/10/2013 18:12, Guenter Roeck wrote:
> On Fri, Jun 21, 2013 at 03:21:28PM -0000, Boris BREZILLON wrote:
>> The at91sam9 watchdog timer can only be configured once, and the current
>> implementation tries to configure it in a static way:
>> - 2 seconds timeout
>> - wdt restart every 500ms
>>
>> If the timer has already been configured with different values, it returns an
>> error and do not create any watchdog device.
>>
>> This is not critical if the watchdog is disabled, but if it has been enabled with
>> different timeout values it will lead to a SoC reset.
>>
>> This patch series tries to address this issue by adapting the heartbeat value
>> according the WDT timer config:
>> - it first tries to configure the timer as requested.
>> - if it fails it fallbacks to the current config, adapting its heartbeat timer
>> to the needs
>>
>> This patch series also move to a dynamically allocated at91wdt device instead
>> of the static instance.
>>
>> It adds a new at91 wdt type: software. This new type make use of the at91 wdt
>> interrupt to trigger a software reboot.
>>
>> Finally it adds several properties to the device tree bindings.
>>
>> Signed-off-by: Boris BREZILLON <b.brezillon@...rkiz.com>
>>
>> ---
>> drivers/watchdog/at91sam9_wdt.c |  319 +++++++++++++++++++++++++++++----------
>>   1 file changed, 236 insertions(+), 83 deletions(-)
>>
>> diff --git a/drivers/watchdog/at91sam9_wdt.c b/drivers/watchdog/at91sam9_wdt.c
>> index be37dde..fb47ec5 100644
>> --- a/drivers/watchdog/at91sam9_wdt.c
>> +++ b/drivers/watchdog/at91sam9_wdt.c
>> @@ -19,11 +19,13 @@
>>   
>>   #include <linux/errno.h>
>>   #include <linux/init.h>
>> +#include <linux/interrupt.h>
>>   #include <linux/io.h>
>>   #include <linux/kernel.h>
>>   #include <linux/module.h>
>>   #include <linux/moduleparam.h>
>>   #include <linux/platform_device.h>
>> +#include <linux/reboot.h>
>>   #include <linux/types.h>
>>   #include <linux/watchdog.h>
>>   #include <linux/jiffies.h>
>> @@ -31,23 +33,32 @@
>>   #include <linux/bitops.h>
>>   #include <linux/uaccess.h>
>>   #include <linux/of.h>
>> +#include <linux/of_address.h>
>> +#include <linux/of_irq.h>
>>   
>>   #include "at91sam9_wdt.h"
>>   
>>   #define DRV_NAME "AT91SAM9 Watchdog"
>>   
>> -#define wdt_read(field) \
>> -	__raw_readl(at91wdt_private.base + field)
>> -#define wdt_write(field, val) \
>> -	__raw_writel((val), at91wdt_private.base + field)
>> +#define wdt_read(wdt, field) \
>> +	__raw_readl((wdt)->base + field)
>> +#define wdt_write(wtd, field, val) \
>> +	__raw_writel((val), (wdt)->base + field)
>>   
>>   /* AT91SAM9 watchdog runs a 12bit counter @ 256Hz,
>>    * use this to convert a watchdog
>>    * value from/to milliseconds.
>>    */
>> +#define hz_to_ticks(h)  (((h << 8) / HZ) - 1)
> Unused.

I'll drop it.

>
>> +#define ticks_to_hz(t)	(((t + 1) * HZ) >> 8)
>>   #define ms_to_ticks(t)	(((t << 8) / 1000) - 1)
>>   #define ticks_to_ms(t)	(((t + 1) * 1000) >> 8)
> You should put macro parameters in () to avoid undesired side effects.
>
> 	(h), (t), (field)
>
> Sure, some of them are old. No reason not to fix it, though.

I'll fix it (I'll fix old macros in a separate patch)

>
>>   
>> +#define WDT_MR_RESET	0x3FFF2FFF
>> +
>> +#define WDT_WDD_MAX	0xFFF
>> +#define WDT_WDV_MAX	0xFFF
> What are the units ?
ticks (slow clk cycles).
I'll rename these macros:
#define WDT_XXX_MAX_TICKS 0xFFF
>
>> +
>>   /* Hardware timeout in seconds */
>>   #define WDT_HW_TIMEOUT 2
>>   
>> @@ -66,23 +77,41 @@ module_param(nowayout, bool, 0);
>>   MODULE_PARM_DESC(nowayout, "Watchdog cannot be stopped once started "
>>   	"(default=" __MODULE_STRING(WATCHDOG_NOWAYOUT) ")");
>>   
>> -static struct watchdog_device at91_wdt_dev;
>> -static void at91_ping(unsigned long data);
>> -
>> -static struct {
>> +#define to_wdt(wdd) container_of(wdd, struct at91wdt, wdd)
>> +struct at91wdt {
>> +	struct watchdog_device wdd;
>>   	void __iomem *base;
>>   	unsigned long next_heartbeat;	/* the next_heartbeat for the timer */
>>   	struct timer_list timer;	/* The timer that pings the watchdog */
>> -} at91wdt_private;
>> +	u32 mr;
>> +	u32 mr_mask;
>> +	unsigned long heartbeat;	/* WDT heartbeat in jiffies */
>> +	bool nowayout;
>> +	unsigned int irq;
>> +};
>>   
>>   /* ......................................................................... */
>>   
>> +static irqreturn_t wdt_interrupt(int irq, void *dev_id)
>> +{
>> +	struct at91wdt *wdt = (struct at91wdt *)dev_id;
>> +
>> +	if (wdt_read(wdt, AT91_WDT_SR)) {
>> +		/* Reboot */
> That is quite obvious, isn't it ?
I'll drop the comment line.
>
>> +		pr_crit("at91sam9 WDT software reset\n");
>> +		emergency_restart();
>> +		pr_crit("Reboot didn't ?????\n");
>> +	}
>> +
>> +	return IRQ_HANDLED;
>> +}
>> +
>>   /*
>>    * Reload the watchdog timer.  (ie, pat the watchdog)
>>    */
>> -static inline void at91_wdt_reset(void)
>> +static inline void at91_wdt_reset(struct at91wdt *wdt)
>>   {
>> -	wdt_write(AT91_WDT_CR, AT91_WDT_KEY | AT91_WDT_WDRSTT);
>> +	wdt_write(wdt, AT91_WDT_CR, AT91_WDT_KEY | AT91_WDT_WDRSTT);
>>   }
>>   
>>   /*
>> @@ -90,26 +119,20 @@ static inline void at91_wdt_reset(void)
>>    */
>>   static void at91_ping(unsigned long data)
>>   {
>> -	if (time_before(jiffies, at91wdt_private.next_heartbeat) ||
>> -	    (!watchdog_active(&at91_wdt_dev))) {
>> -		at91_wdt_reset();
>> -		mod_timer(&at91wdt_private.timer, jiffies + WDT_TIMEOUT);
>> +	struct at91wdt *wdt = (struct at91wdt *)data;
>> +	if (time_before(jiffies, wdt->next_heartbeat) ||
>> +	    (!watchdog_active(&wdt->wdd))) {
>
> 	Unnecessary () around !watchdog_active()
>
> [ Sure, old code. Not a reason not to clean it up ]
Okay, I'll remove all unnecessary "()" (even the old ones).
>
>> +		at91_wdt_reset(wdt);
>> +		mod_timer(&wdt->timer, jiffies + wdt->heartbeat);
>>   	} else
>>   		pr_crit("I will reset your machine !\n");
>>   }
>>   
>>   static int at91_wdt_ping(struct watchdog_device *wdd)
>>   {
>> +	struct at91wdt *wdt = to_wdt(wdd);
>>   	/* calculate when the next userspace timeout will be */
>> -	at91wdt_private.next_heartbeat = jiffies + wdd->timeout * HZ;
>> -	return 0;
>> -}
>> -
>> -static int at91_wdt_start(struct watchdog_device *wdd)
>> -{
>> -	/* calculate the next userspace timeout and modify the timer */
>> -	at91_wdt_ping(wdd);
>> -	mod_timer(&at91wdt_private.timer, jiffies + WDT_TIMEOUT);
>> +	wdt->next_heartbeat = jiffies + wdd->timeout * HZ;
>>   	return 0;
>>   }
>>   
>> @@ -125,36 +148,82 @@ static int at91_wdt_set_timeout(struct watchdog_device *wdd, unsigned int new_ti
>>   	return 0;
>>   }
>>   
>> -/*
>> - * Set the watchdog time interval in 1/256Hz (write-once)
>> - * Counter is 12 bit.
>> - */
>> -static int at91_wdt_settimeout(unsigned int timeout)
>> +static int at91_wdt_init(struct platform_device *pdev, struct at91wdt *wdt)
>>   {
>> -	unsigned int reg;
>> -	unsigned int mr;
>> -
>> -	/* Check if disabled */
>> -	mr = wdt_read(AT91_WDT_MR);
>> -	if (mr & AT91_WDT_WDDIS) {
>> -		pr_err("sorry, watchdog is disabled\n");
>> -		return -EIO;
>> +	u32 tmp;
>> +	u32 delta;
>> +	u32 value;
>> +	int err;
>> +	u32 mask = wdt->mr_mask;
>> +
>> +	tmp = wdt_read(wdt, AT91_WDT_MR);
>> +	if ((tmp & mask) != (wdt->mr & mask)) {
>> +		if (tmp == WDT_MR_RESET) {
>> +			wdt_write(wdt, AT91_WDT_MR, wdt->mr);
>> +			tmp = wdt_read(wdt, AT91_WDT_MR);
>> +		}
>> +	}
>> +
>> +	if (tmp & AT91_WDT_WDDIS) {
>> +		if (wdt->mr & AT91_WDT_WDDIS)
>> +			return 0;
>> +		dev_err(wdt->wdd.parent,
>> +			": sorry, watchdog is disabled\n");
> No need to be sorry all the time. The ':' is unnecessary.

Sure, I'll remove the ":" and rework old and new messages (remove the 
"sorry" word).
>
>> +		return -EINVAL;
>> +	}
>> +
>> +	value = tmp & AT91_WDT_WDV;
>> +	delta = (tmp & AT91_WDT_WDD) >> 16;
>> +
>> +	if (delta < value) {
>> +		if ((value / (value - delta)) < 4) {
> 	Unnecessary ( ) around left side of equation.
>
>> +			dev_err(wdt->wdd.parent,
>> +				": sorry, max-heartbeat should be at least 4 times min-heartbeat (max-heartbeat = %d x min-heartbeat)\n",
>> +				(value / (value - delta)));
> 	Unnecessary ( ) around the equation.
>
>> +			return -EINVAL;
>> +		}
>> +	}
>> +
>> +	wdt->heartbeat = ticks_to_hz(value / 4);
>> +
>> +	if (!wdt->heartbeat) {
>> +		dev_err(wdt->wdd.parent,
>> +			": sorry, linux timer (%i Hz) cannot handle watchdog timeout (%i ms)\n",
>> +			HZ, ticks_to_ms(value));
>> +		return -EINVAL;
> Isn't that a bit rude ? Why not set it to the minimum ?
We're using a normal timer (not an hrtimer), and IIRC normal timers' 
precision depends on the
configured HZ option. As a result the minimum heartbeat value may 
trigger the timer function
after the hardware watchdog counter expires.

An example where this problem might occur:

HZ = 10 <=> normal timer precision = 100 ms
min hearbeat = 180 ms
max hearbeat = 200 ms

The div by 4 operation is here to take a safety margin by refreshing the 
hardware counter at least
4 times more often than needed.

I'll think of something more flexible...
If you have some ideas, please feel free to share it.

>> +	}
>> +
>> +	if ((tmp & AT91_WDT_WDFIEN) && wdt->irq) {
>> +		err = request_irq(wdt->irq, wdt_interrupt,
>> +				  IRQF_SHARED | IRQF_IRQPOLL,
>> +				  pdev->name, wdt);
>> +		if (err)
>> +			return err;
>>   	}
>>   
>> -	/*
>> -	 * All counting occurs at SLOW_CLOCK / 128 = 256 Hz
>> -	 *
>> -	 * Since WDV is a 12-bit counter, the maximum period is
>> -	 * 4096 / 256 = 16 seconds.
>> -	 */
>> -	reg = AT91_WDT_WDRSTEN	/* causes watchdog reset */
>> -		/* | AT91_WDT_WDRPROC	causes processor reset only */
>> -		| AT91_WDT_WDDBGHLT	/* disabled in debug mode */
>> -		| AT91_WDT_WDD		/* restart at any time */
>> -		| (timeout & AT91_WDT_WDV);  /* timer value */
>> -	wdt_write(AT91_WDT_MR, reg);
>> +	if ((tmp & wdt->mr_mask) != (wdt->mr & wdt->mr_mask))
>> +		dev_warn(wdt->wdd.parent,
>> +			 ": watchdog already configured differently (mr = %x expecting %x)\n",
>> +			 tmp & wdt->mr_mask, wdt->mr & wdt->mr_mask);
>> +
>> +	setup_timer(&wdt->timer, at91_ping, (unsigned long)wdt);
>> +	mod_timer(&wdt->timer, jiffies + wdt->heartbeat);
>> +
>> +	/* Try to set timeout from device tree first */
>> +	if (watchdog_init_timeout(&wdt->wdd, 0, &pdev->dev))
>> +		watchdog_init_timeout(&wdt->wdd, heartbeat, &pdev->dev);
>> +	watchdog_set_nowayout(&wdt->wdd, wdt->nowayout);
>> +	err = watchdog_register_device(&wdt->wdd);
>> +	if (err)
>> +		goto out_stop_timer;
>> +
>> +	wdt->next_heartbeat = jiffies + wdt->wdd.timeout * HZ;
>>   
>>   	return 0;
>> +
>> +out_stop_timer:
>> +	del_timer(&wdt->timer);
>> +	return err;
>>   }
>>   
>>   /* ......................................................................... */
>> @@ -167,63 +236,147 @@ static const struct watchdog_info at91_wdt_info = {
>>   
>>   static const struct watchdog_ops at91_wdt_ops = {
>>   	.owner =	THIS_MODULE,
>> -	.start =	at91_wdt_start,
>> +	.start =	at91_wdt_ping,
>>   	.stop =		at91_wdt_stop,
>>   	.ping =		at91_wdt_ping,
>>   	.set_timeout =	at91_wdt_set_timeout,
>>   };
>>   
>> -static struct watchdog_device at91_wdt_dev = {
>> -	.info =		&at91_wdt_info,
>> -	.ops =		&at91_wdt_ops,
>> -	.timeout =	WDT_HEARTBEAT,
>> -	.min_timeout =	1,
>> -	.max_timeout =	0xFFFF,
>> -};
>> +#if defined(CONFIG_OF)
>> +static int of_at91wdt_init(struct device_node *np, struct at91wdt *wdt)
>> +{
>> +	u32 min = 0;
>> +	u32 max = 0xFFF;
> Are those default values ? If so might use defines (there are actually defines
> for 0xfff already).
I'll replace the 0xfff value by the XX_MAX macro.
Should I create a new XX_MIN macro ?
>> +	const char *tmp;
>> +
>> +	wdt->base = of_iomap(np, 0);
> I am a bit at loss why you need to use use this function here.
>
> I think it would be more beneficial to use devm_ioremap() or even better
> devm_ioremap_resource() in both of and non-dt cases; then you don't have
> to call iounmap().

Sure. This was one of my first driver using the devm and of_iomap 
functions, and now I realize
I've been misusing them.

I'll fix this too.

>> +	if (!wdt->base) {
>> +		dev_err(wdt->wdd.parent, "failed to map registers, aborting.\n");
>> +		return -EINVAL;
>> +	}
>> +
>> +	/* Get the interrupts property */
>> +	wdt->irq = irq_of_parse_and_map(np, 0);
>> +	if (!wdt->irq)
>> +		dev_warn(wdt->wdd.parent, "failed to get IRQ from DT.\n");
>> +
>> +	if (!of_property_read_u32_index(np, "atmel,max-heartbeat-sec", 0,
>> +					&max)) {
>> +		max *= 256;
>> +		if (max > WDT_WDV_MAX)
>> +			max = WDT_WDV_MAX;
>> +
>> +		if (!of_property_read_u32_index(np, "atmel,min-heartbeat-sec",
>> +						0, &min)) {
>> +			min *= 256;
>> +			if (4 * min > max)
>> +				min = max / 4;
>> +		}
>> +	}
> I am a bit confused about those parameters. How do they match min_timeout and
> max_timeout ?

AT91 wdt block does not provide a reconfigurable timeout.
To bypass this limitation the driver periodically reset the hw watchdog 
(based on the previous config,
the device tree config or the static config) using a timer.

The ping callback (used by watchdog core) only compute the 
next_heartbeat (expressed in system ticks)
based on the current jiffies value (number of ticks elapsed since system 
startup) and the configured
timeout value (configured using the set_timeout callback).

To summarize:
  - min/max heartbeat timeout represent the hw timeout properties (those 
directly linked to WDD WDV
    fields).
  - min/max timeout (in watchdog_device struct) represent the software 
timeout properties (those
    exposed to the user space API).

I could rework the driver to directly use the hw properties and remove 
the set_timeout functionality,
but this would break the user space API.

>> +
>> +	wdt->mr_mask = 0x3FFFFFFF;
>> +	wdt->mr = 0;
>> +	if (!of_property_read_string(np, "atmel,watchdog-type", &tmp) &&
>> +	    !strcmp(tmp, "software")) {
>> +		wdt->mr |= AT91_WDT_WDFIEN;
>> +		wdt->mr_mask &= ~AT91_WDT_WDRPROC;
>> +	} else
>> +		wdt->mr |= AT91_WDT_WDRSTEN;
>> +
>> +	if (!of_property_read_string(np, "atmel,reset-type", &tmp) &&
>> +	    !strcmp(tmp, "proc"))
>> +		wdt->mr |= AT91_WDT_WDRPROC;
>> +
>> +	if (of_property_read_bool(np, "atmel,disable")) {
>> +		wdt->mr |= AT91_WDT_WDDIS;
>> +		wdt->mr_mask &= AT91_WDT_WDDIS;
>> +	}
>> +
>> +	if (of_property_read_bool(np, "atmel,idle-halt"))
>> +		wdt->mr |= AT91_WDT_WDIDLEHLT;
>> +
>> +	if (of_property_read_bool(np, "atmel,dbg-halt"))
>> +		wdt->mr |= AT91_WDT_WDDBGHLT;
>> +
>> +	wdt->mr |= max | ((max - min) << 16);
>> +
>> +	return 0;
>> +}
>> +#else
>> +static inline int of_at91wdt_init(struct device_node *np, struct at91wdt *wdt)
>> +{
>> +	return 0;
>> +}
>> +#endif
>>   
>>   static int __init at91wdt_probe(struct platform_device *pdev)
>>   {
>>   	struct resource	*r;
>> -	int res;
>> -
>> -	r = platform_get_resource(pdev, IORESOURCE_MEM, 0);
>> -	if (!r)
>> -		return -ENODEV;
>> -	at91wdt_private.base = ioremap(r->start, resource_size(r));
>> -	if (!at91wdt_private.base) {
>> -		dev_err(&pdev->dev, "failed to map registers, aborting.\n");
>> -		return -ENOMEM;
>> -	}
>> +	int err;
>> +	struct at91wdt *wdt;
>>   
>> -	at91_wdt_dev.parent = &pdev->dev;
>> -	watchdog_init_timeout(&at91_wdt_dev, heartbeat, &pdev->dev);
>> -	watchdog_set_nowayout(&at91_wdt_dev, nowayout);
>> +	wdt = devm_kzalloc(&pdev->dev, sizeof(*wdt), GFP_KERNEL);
>> +	if (!wdt)
>> +		return -ENOMEM;
>>   
>> -	/* Set watchdog */
>> -	res = at91_wdt_settimeout(ms_to_ticks(WDT_HW_TIMEOUT * 1000));
>> -	if (res)
>> -		return res;
>> +	wdt->mr = (WDT_HW_TIMEOUT * 256) | AT91_WDT_WDRSTEN | AT91_WDT_WDD |
>> +		  AT91_WDT_WDDBGHLT | AT91_WDT_WDIDLEHLT;
>> +	wdt->mr_mask = 0x3FFFFFFF;
>> +	wdt->nowayout = nowayout;
>> +	wdt->wdd.parent = &pdev->dev;
>> +	wdt->wdd.info = &at91_wdt_info;
>> +	wdt->wdd.ops = &at91_wdt_ops;
>> +	wdt->wdd.timeout = WDT_HEARTBEAT;
>> +	wdt->wdd.min_timeout = 1;
>> +	wdt->wdd.max_timeout = 0xFFFF;
>> +
>> +	if (pdev->dev.of_node) {
>> +		err = of_at91wdt_init(pdev->dev.of_node, wdt);
>> +		if (err)
>> +			goto out_free_watchdog;
>> +	} else {
>> +		r = platform_get_resource(pdev, IORESOURCE_MEM, 0);
>> +		if (!r) {
>> +			err = -ENODEV;
>> +			goto out_free_watchdog;
>> +		}
>> +
>> +		wdt->base = ioremap(r->start, resource_size(r));
>> +		if (!wdt->base) {
>> +			dev_err(&pdev->dev, "failed to map registers, aborting.\n");
>> +			err = -ENOMEM;
>> +			goto out_free_watchdog;
>> +		}
>> +	}
>>   
>> -	res = watchdog_register_device(&at91_wdt_dev);
>> -	if (res)
>> -		return res;
>> +	err = at91_wdt_init(pdev, wdt);
>> +	if (err)
>> +		goto out_iounmap;
>>   
>> -	at91wdt_private.next_heartbeat = jiffies + at91_wdt_dev.timeout * HZ;
>> -	setup_timer(&at91wdt_private.timer, at91_ping, 0);
>> -	mod_timer(&at91wdt_private.timer, jiffies + WDT_TIMEOUT);
>> +	platform_set_drvdata(pdev, wdt);
>>   
>>   	pr_info("enabled (heartbeat=%d sec, nowayout=%d)\n",
>> -		at91_wdt_dev.timeout, nowayout);
>> +		wdt->wdd.timeout, wdt->nowayout);
>>   
>>   	return 0;
>> +
>> +out_iounmap:
>> +	iounmap(wdt->base);
>> +out_free_watchdog:
>> +	devm_kfree(&pdev->dev, wdt);
> The whole point of using devm_kzalloc() is that you don't have to call kfree()
> or devm_kfree(). So this call (and with it the label) is unnecessary.
>
>> +	return err;
>>   }
>>   
>>   static int __exit at91wdt_remove(struct platform_device *pdev)
>>   {
>> -	watchdog_unregister_device(&at91_wdt_dev);
>> +	struct at91wdt *wdt = platform_get_drvdata(pdev);
>> +	watchdog_unregister_device(&wdt->wdd);
>>   
>>   	pr_warn("I quit now, hardware will probably reboot!\n");
>> -	del_timer(&at91wdt_private.timer);
>> +	del_timer(&wdt->timer);
>> +
>> +	iounmap(wdt->base);
>> +	devm_kfree(&pdev->dev, wdt);
>>   
> The call to devm_kfree() is unnecessary.
>
>>   	return 0;
>>   }

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