Re: [v2,1/4] watchdog: at91sam9_wdt: better watchdog support

[Guenter Roeck]

On Wed, Oct 02, 2013 at 09:27:03PM +0200, boris brezillon wrote:
> 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@xxxxxxxxxxx>
> >>
> >>---
> >>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
> 

Seems to me those values are not really reasonable to start with. From a Linux
perspective, the minimum timeout will never be less than 1 second.

In the given context (HZ=10, as unlikely it might be), you might consider
setting accepted minimum to 400ms. The maximum should then be at least 1,600ms
anyway, correct ?

Thanks,
Guenter

> 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;
> >>  }
> 
> 
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/