Re: [PATCH v2] TCO watchdog pretimeout handler

From: Guenter Roeck
Date: Wed Jun 17 2015 - 01:15:28 EST

On 06/16/2015 06:45 AM, Francois-Nicolas Muller wrote:
Use TCO watchdog first timeout (pretimeout) to dump CPU backtraces
and ease debug of watchdog expiration causes.
TCO logic generates a SCI interrupt, then its handler dumps all CPU
backtraces and calls panic (in order to execute registered panic
SCI interrupt number (GPE) is configured from ACPI tables.

Signed-off-by: Francois-Nicolas Muller <francois-nicolas.muller@xxxxxxxxx>
Thanks Guenter for your review.

If I recall correctly, the iTCO watchdog can also generate an NMI.
Would it make sense to add support for handling this NMI as well ?

As far as I know, there is no NMI option for TCO watchdog interrupt.
Do you have any documentation about this ?

Actually that was a miscommunication, sorry. I confused it waith another watchdog.

I assume you took out all mention of SMI because it is not (yet) supported.
Would be interesting to know what systems out there actually use / configure.

Here is a new version (v2) of the patch:
- rebased on latest kernel
- fixed coding style issues

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..cd2569a 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);
"Turn off SMI clearing watchdog (depends on TCO-version)(default=1)");

+static bool pretimeout = DEFAULT_PRETIMEOUT;
+module_param(pretimeout, bool, 0);
+MODULE_PARM_DESC(pretimeout, "Enable watchdog pretimeout (default="
* 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";

Do people understand what this means ? Is that some Intel magic string ?
Does this work for all instances of iTCO watchdogs, or only for a specific
system or iTCO version ?

Rafael asked this question as well, but I don't recall seeing an answer.

I see that it maps to a PCI ID for Intel Braswell, but I have no idea
how that translates to something useful for ACPI. Is this a well defined
(and allocated) ACPI HID ? How about other chips (non-Braswell)
which are supported by this driver ?

+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");
+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);

Do we know for sure that _GPE is always associated with the watchdog ?
Is that because of tco_hid ?


+ 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;

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at