[PATCH v2] watchdog: iTCO_wdt: Account for rebooting on second timeout

[Jan Kiszka <jan.kiszka@siemens.com>]

From: Jan Kiszka <jan.kiszka@siemens.com>

This was already attempted to fix via 1fccb73011ea: If the BIOS did not
enable TCO SMIs, the timer definitely needs to trigger twice in order to
cause a reboot. If TCO SMIs are on, as well as SMIs in general, we can
continue to assume that the BIOS will perform a reboot on the first
timeout.

QEMU with its ICH9 and related BIOS falls into the former category,
currently taking twice the configured timeout in order to reboot the
machine. For iTCO version that fall under turn_SMI_watchdog_clear_off,
this is also true and was currently only addressed for v1, irrespective
of the turn_SMI_watchdog_clear_off value.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---

Changes in v2:
 - consider GBL_SMI_EN as well

 drivers/watchdog/iTCO_wdt.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/watchdog/iTCO_wdt.c b/drivers/watchdog/iTCO_wdt.c
index bf31d7b67a69..3f1324871cfd 100644
--- a/drivers/watchdog/iTCO_wdt.c
+++ b/drivers/watchdog/iTCO_wdt.c
@@ -71,6 +71,8 @@
 #define TCOBASE(p)	((p)->tco_res->start)
 /* SMI Control and Enable Register */
 #define SMI_EN(p)	((p)->smi_res->start)
+#define TCO_EN		(1 << 13)
+#define GBL_SMI_EN	(1 << 0)
 
 #define TCO_RLD(p)	(TCOBASE(p) + 0x00) /* TCO Timer Reload/Curr. Value */
 #define TCOv1_TMR(p)	(TCOBASE(p) + 0x01) /* TCOv1 Timer Initial Value*/
@@ -355,8 +357,12 @@ static int iTCO_wdt_set_timeout(struct watchdog_device *wd_dev, unsigned int t)
 
 	tmrval = seconds_to_ticks(p, t);
 
-	/* For TCO v1 the timer counts down twice before rebooting */
-	if (p->iTCO_version == 1)
+	/*
+	 * If TCO SMIs are off, the timer counts down twice before rebooting.
+	 * Otherwise, the BIOS generally reboots when the SMI triggers.
+	 */
+	if (p->smi_res &&
+	    (SMI_EN(p) & (TCO_EN | GBL_SMI_EN)) != (TCO_EN | GBL_SMI_EN))
 		tmrval /= 2;
 
 	/* from the specs: */
@@ -521,7 +527,7 @@ static int iTCO_wdt_probe(struct platform_device *pdev)
 		 * Disables TCO logic generating an SMI#
 		 */
 		val32 = inl(SMI_EN(p));
-		val32 &= 0xffffdfff;	/* Turn off SMI clearing watchdog */
+		val32 &= ~TCO_EN;	/* Turn off SMI clearing watchdog */
 		outl(val32, SMI_EN(p));
 	}
 
-- 
2.26.2