[PATCH v3] TCO watchdog pretimeout handler

[Francois-Nicolas Muller]

Use TCO watchdog first timeout (pretimeout) to dump CPU backtraces
and ease debug of watchdog expiration causes.
On Intel Cherrytrail, TCO logic generates a SMI, then SMI handler
triggers a SCI to the kernel, on a specific GPE.
The GPE handler dumps all CPU backtraces and calls panic (in order
to execute registered panic callbacks).
GPE number is configured from ACPI tables if LPC HID exists.

Signed-off-by: Francois-Nicolas Muller <francois-nicolas.muller@xxxxxxxxx>
---
SMI is not supported by the driver, only SCI.

On Intel Cherrytrail, TCO watchdog raises an SMI, then the SMI handler
in Bios trigs a SCI to the kernel (in Android OS configuration).

The patch has some effect only on Cherrytrail platform.
On Braswell, the TCO HID exists in ACPI tables, so SCI is configured. But
the SMI handler does not trig the SCI.
On other platforms, the HID does not exist in ACPI tables, and the SMI
handler does not trig the SCI.

In ACPI tables, _GPE is associated to this HID, so no possible confusion.

FranÃois-Nicolas
---
 drivers/watchdog/iTCO_wdt.c | 50 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 50 insertions(+)

diff --git a/drivers/watchdog/iTCO_wdt.c b/drivers/watchdog/iTCO_wdt.c
index 3c3fd41..3e9ec8b 100644
--- a/drivers/watchdog/iTCO_wdt.c
+++ b/drivers/watchdog/iTCO_wdt.c
@@ -68,6 +68,8 @@
 #include <linux/io.h>			/* For inb/outb/... */
 #include <linux/mfd/core.h>
 #include <linux/mfd/lpc_ich.h>
+#include <linux/nmi.h>
+#include <linux/acpi.h>
 
 #include "iTCO_vendor.h"
 
@@ -127,6 +129,12 @@ module_param(turn_SMI_watchdog_clear_off, int, 0);
 MODULE_PARM_DESC(turn_SMI_watchdog_clear_off,
 	"Turn off SMI clearing watchdog (depends on TCO-version)(default=1)");
 
+#define DEFAULT_PRETIMEOUT 0
+static bool pretimeout = DEFAULT_PRETIMEOUT;
+module_param(pretimeout, bool, 0);
+MODULE_PARM_DESC(pretimeout, "Enable watchdog pretimeout (default="
+				__MODULE_STRING(DEFAULT_PRETIMEOUT) ")");
+
 /*
  * Some TCO specific functions
  */
@@ -201,6 +209,45 @@ static int iTCO_wdt_unset_NO_REBOOT_bit(void)
 	return ret; /* returns: 0 = OK, -EIO = Error */
 }
 
+static unsigned char *tco_hid = "8086229C"; /* Intel Cherrytrail LPC */
+
+static u32 iTCO_wdt_pretimeout_handler(acpi_handle gpe_device, u32 gpe,
+				       void *context)
+{
+	/* dump backtraces for all available cores */
+	trigger_all_cpu_backtrace();
+
+	/* call panic notifiers */
+	panic("Kernel Watchdog");
+
+	return ACPI_INTERRUPT_HANDLED;
+}
+
+static acpi_status __init iTCO_wdt_register_gpe(acpi_handle handle,
+					u32 lvl, void *context, void **rv)
+{
+	unsigned long long gpe;
+	acpi_status status;
+	union acpi_object object = { 0 };
+	struct acpi_buffer buffer = { sizeof(union acpi_object), &object };
+
+	status = acpi_evaluate_object(handle, "_GPE", NULL, &buffer);
+	if (ACPI_FAILURE(status))
+		return status;
+
+	if (object.type != ACPI_TYPE_INTEGER)
+		return AE_BAD_DATA;
+
+	gpe = object.integer.value;
+	status = acpi_install_gpe_handler(NULL, gpe, ACPI_GPE_EDGE_TRIGGERED,
+					  iTCO_wdt_pretimeout_handler, NULL);
+	if (ACPI_FAILURE(status))
+		return status;
+
+	acpi_enable_gpe(NULL, gpe);
+	return AE_OK;
+}
+
 static int iTCO_wdt_start(struct watchdog_device *wd_dev)
 {
 	unsigned int val;
@@ -641,6 +688,9 @@ static int __init iTCO_wdt_init_module(void)
 	if (err)
 		return err;
 
+	if (pretimeout)
+		acpi_get_devices(tco_hid, iTCO_wdt_register_gpe, NULL, NULL);
+
 	return 0;
 }
 
-- 
1.9.1

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