[PATCH] m8xx_wdt: software watchdog reset/interrupt select

[Marcelo Tosatti <marcelo.tosatti@cyclades.com>]

Hi,

Currently the mpc8xx_wdt driver installs an IRQ handler for
PIT_INTERRUPT (SIU_LEVEL0, irq 1) to service the WDT until a userspace
watchdog daemon takes over after boot.

However, if the "software watchdog reset/interrupt select" (SWRI) bit of
SYPCR register is set, no interrupt is generated. In that configuration
(the default) HRESET signal is generated if the WDT timeout expires,
without kernel notification.

The following patch creates a kernel timer to service the WDT and rearm
itself in case this configuration is detected, making it possible to
boot the system with the watchdog turned on. The timer is shutdown
once the userspace daemon open's the device.

Note: From my reading of the documentation, even if the SWRI bit is
unset (interrupt select mode), an NMI at IRQ0 should cause the system to
jump to exception vector 0x100, resetting the system.

So I'm wondering if the interrupt mode ever worked?


--- ../git/linux-2.6/arch/ppc/syslib/m8xx_wdt.c	2005-11-08 11:38:39.000000000 -0600
+++ linux-2.6-git-wednov02/arch/ppc/syslib/m8xx_wdt.c	2005-11-14 10:36:53.000000000 -0600
@@ -45,35 +45,18 @@
 	return IRQ_HANDLED;
 }
 
-void __init m8xx_wdt_handler_install(bd_t * binfo)
+#define SYPCR_SWP 0x1
+#define SYPCR_SWRI 0x2
+#define SYPCR_SWE 0x4
+
+/* software watchdog reset/interrupt select */
+int m8xx_wdt_keepalive_mode = 0;
+
+void __init m8xx_wdt_install_irq(volatile immap_t *imap, bd_t *binfo)
 {
-	volatile immap_t *imap = (volatile immap_t *)IMAP_ADDR;
 	u32 pitc;
-	u32 sypcr;
 	u32 pitrtclk;
 
-	sypcr = in_be32(&imap->im_siu_conf.sc_sypcr);
-
-	if (!(sypcr & 0x04)) {
-		printk(KERN_NOTICE "m8xx_wdt: wdt disabled (SYPCR: 0x%08X)\n",
-		       sypcr);
-		return;
-	}
-
-	m8xx_wdt_reset();
-
-	printk(KERN_NOTICE
-	       "m8xx_wdt: active wdt found (SWTC: 0x%04X, SWP: 0x%01X)\n",
-	       (sypcr >> 16), sypcr & 0x01);
-
-	wdt_timeout = (sypcr >> 16) & 0xFFFF;
-
-	if (!wdt_timeout)
-		wdt_timeout = 0xFFFF;
-
-	if (sypcr & 0x01)
-		wdt_timeout *= 2048;
-
 	/*
 	 * Fire trigger if half of the wdt ticked down 
 	 */
@@ -98,6 +81,66 @@
 	printk(KERN_NOTICE
 	       "m8xx_wdt: keep-alive trigger installed (PITC: 0x%04X)\n", pitc);
 
+}
+
+static void m8xx_wdt_timer_func(unsigned long data);
+
+static struct timer_list m8xx_wdt_timer =
+	TIMER_INITIALIZER(m8xx_wdt_timer_func, 0, 0);
+
+void m8xx_wdt_stop_timer(void)
+{
+	del_timer(&m8xx_wdt_timer);
+}
+
+static void m8xx_wdt_timer_func(unsigned long data)
+{
+	m8xx_wdt_reset();
+	m8xx_wdt_timer.expires = jiffies + 25;
+	add_timer(&m8xx_wdt_timer);
+}
+
+void m8xx_wdt_install_timer(volatile immap_t *imap)
+{
+	m8xx_wdt_timer.expires = jiffies + 25;
+	add_timer(&m8xx_wdt_timer);
+}
+
+void __init m8xx_wdt_handler_install(bd_t * binfo)
+{
+	volatile immap_t *imap = (volatile immap_t *)IMAP_ADDR;
+	u32 sypcr;
+
+	sypcr = in_be32(&imap->im_siu_conf.sc_sypcr);
+
+	printk(KERN_NOTICE "m8xx_wdt SYPCR: 0x%08X)\n", sypcr);
+
+	if (!(sypcr & SYPCR_SWE)) {
+		printk(KERN_NOTICE "m8xx_wdt: wdt disabled (SYPCR: 0x%08X)\n",
+		       sypcr);
+		return;
+	}
+
+	m8xx_wdt_reset();
+
+	printk(KERN_NOTICE
+	       "m8xx_wdt: active wdt found (SWTC: 0x%04X, SWP: 0x%01X)\n",
+	       (sypcr >> 16), sypcr & SYPCR_SWP);
+
+	wdt_timeout = (sypcr >> 16) & 0xFFFF;
+
+	if (!wdt_timeout)
+		wdt_timeout = 0xFFFF;
+
+	if (sypcr & SYPCR_SWP)
+		wdt_timeout *= 2048;
+
+	m8xx_wdt_keepalive_mode = sypcr & SYPCR_SWRI;
+	if (m8xx_wdt_keepalive_mode)
+		m8xx_wdt_install_timer(imap);
+	else
+		m8xx_wdt_install_irq(imap, binfo);
+
 	wdt_timeout /= binfo->bi_intfreq;
 }
 
--- ../git/linux-2.6/arch/ppc/syslib/m8xx_wdt.h	2005-10-10 18:06:12.000000000 -0500
+++ linux-2.6-git-wednov02/arch/ppc/syslib/m8xx_wdt.h	2005-11-14 10:37:39.000000000 -0600
@@ -9,8 +9,12 @@
 #ifndef _PPC_SYSLIB_M8XX_WDT_H
 #define _PPC_SYSLIB_M8XX_WDT_H
 
+extern int m8xx_wdt_keepalive_mode;
+
 extern void m8xx_wdt_handler_install(bd_t * binfo);
 extern int m8xx_wdt_get_timeout(void);
 extern void m8xx_wdt_reset(void);
+extern void m8xx_wdt_install_timer(volatile immap_t *imap);
+extern void m8xx_wdt_stop_timer(void);
 
 #endif				/* _PPC_SYSLIB_M8XX_WDT_H */
--- ../git/linux-2.6/drivers/char/watchdog/mpc8xx_wdt.c	2005-10-10 18:06:15.000000000 -0500
+++ linux-2.6-git-wednov02/drivers/char/watchdog/mpc8xx_wdt.c	2005-11-14 10:37:15.000000000 -0600
@@ -27,7 +27,10 @@
 {
 	volatile immap_t *imap = (volatile immap_t *)IMAP_ADDR;
 
-	imap->im_sit.sit_piscr &= ~(PISCR_PIE | PISCR_PTE);
+	if (m8xx_wdt_keepalive_mode)
+		m8xx_wdt_stop_timer();
+	else
+		imap->im_sit.sit_piscr &= ~(PISCR_PIE | PISCR_PTE);
 
 	printk(KERN_NOTICE "mpc8xx_wdt: keep-alive handler deactivated\n");
 }
@@ -36,7 +39,10 @@
 {
 	volatile immap_t *imap = (volatile immap_t *)IMAP_ADDR;
 
-	imap->im_sit.sit_piscr |= PISCR_PIE | PISCR_PTE;
+	if (m8xx_wdt_keepalive_mode)
+		m8xx_wdt_install_timer(imap);
+	else
+		imap->im_sit.sit_piscr |= PISCR_PIE | PISCR_PTE;
 
 	printk(KERN_NOTICE "mpc8xx_wdt: keep-alive handler activated\n");
 }