PM: dpm_watchdog: add module param to backtrace all CPUs

Add dpm_watchdog_all_cpu_backtrace module parameter which
controls all CPU backtrace dump before the DPM watchdog panics
the system.

This is expected to help understand what might have caused device
timeout.

Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Reviewed-by: Tomasz Figa <tfiga@chromium.org>
Reviewed-by: Dhruva Gole <d-gole@ti.com>
Link: https://patch.msgid.link/20251007063551.3147937-1-senozhatsky@chromium.org
[ rjw: Subject and changelog edits ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Author: sergey-senozhatsky

drivers/base/power/main.c

@@ -34,6 +34,7 @@
 #include <linux/cpufreq.h>
 #include <linux/devfreq.h>
 #include <linux/timer.h>
+#include <linux/nmi.h>
 
 #include "../base.h"
 #include "power.h"
@@ -515,6 +516,11 @@ struct dpm_watchdog {
 #define DECLARE_DPM_WATCHDOG_ON_STACK(wd) \
 	struct dpm_watchdog wd
 
+static bool __read_mostly dpm_watchdog_all_cpu_backtrace;
+module_param(dpm_watchdog_all_cpu_backtrace, bool, 0644);
+MODULE_PARM_DESC(dpm_watchdog_all_cpu_backtrace,
+		 "Backtrace all CPUs on DPM watchdog timeout");
+
 /**
  * dpm_watchdog_handler - Driver suspend / resume watchdog handler.
  * @t: The timer that PM watchdog depends on.
@@ -530,8 +536,12 @@ static void dpm_watchdog_handler(struct timer_list *t)
 	unsigned int time_left;
 
 	if (wd->fatal) {
+		unsigned int this_cpu = smp_processor_id();
+
 		dev_emerg(wd->dev, "**** DPM device timeout ****\n");
 		show_stack(wd->tsk, NULL, KERN_EMERG);
+		if (dpm_watchdog_all_cpu_backtrace)
+			trigger_allbutcpu_cpu_backtrace(this_cpu);
 		panic("%s %s: unrecoverable failure\n",
 			dev_driver_string(wd->dev), dev_name(wd->dev));
 	}