[PATCH] intel_idle: Handle older CPUs, which stop the TSC in deeper C states, correctly

Thomas Gleixner
2025-02-25T22:37:11Z

The Intel idle driver is preferred over the ACPI processor idle driver,
but fails to implement the work around for Core2 generation CPUs, where
the TSC stops in C2 and deeper C-states. This causes stalls and boot
delays, when the clocksource watchdog does not catch the unstable TSC
before the CPU goes deep idle for the first time.

The ACPI driver marks the TSC unstable when it detects that the CPU
supports C2 or deeper and the CPU does not have a non-stop TSC.

Add the equivivalent work around to the Intel idle driver to cure that.

Fixes: 18734958e9bf ("intel_idle: Use ACPI _CST for processor models without C-state tables")
Reported-by: Fab Stz <fabstz-it@yahoo.fr>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Fab Stz <fabstz-it@yahoo.fr>
Cc: stable@vger.kernel.org
Closes: https://lore.kernel.org/all/10cf96aa-1276-4bd4-8966-c890377030c3@yahoo.fr
---
drivers/idle/intel_idle.c | 4 ++++
1 file changed, 4 insertions(+)

--- a/drivers/idle/intel_idle.c
+++ b/drivers/idle/intel_idle.c
@@ -56,6 +56,7 @@
#include <asm/intel-family.h>
#include <asm/mwait.h>
#include <asm/spec-ctrl.h>
+#include <asm/tsc.h>
#include <asm/fpu/api.h>

#define INTEL_IDLE_VERSION "0.5.1"
@@ -1799,6 +1800,9 @@ static void __init intel_idle_init_cstat
if (intel_idle_state_needs_timer_stop(state))
state->flags |= CPUIDLE_FLAG_TIMER_STOP;

+ if (cx->type > ACPI_STATE_C1 && !boot_cpu_has(X86_FEATURE_NONSTOP_TSC))
+ mark_tsc_unstable("TSC halts in idle");
+
state->enter = intel_idle;
state->enter_s2idle = intel_idle_s2idle;
}