On Sat, Oct 24, 2020 at 6:27 PM Chen Yu yu.c.chen@intel.com wrote:

Currently intel_idle driver gets the c-state information from ACPI _CST if the processor model is not recognized by it. However the c-state in _CST starts with index 1 which is different from the index in intel_idle driver's internal c-state table. While intel_idle_max_cstate_reached() was previously introduced to deal with intel_idle driver's internal c-state table, re-using this function directly on _CST might get wrong. Fix this by subtracting the index by 1 when checking max cstate via _CST. For example, append intel_idle.max_cstate=1 in boot command line, Before the patch: grep . /sys/devices/system/cpu/cpu0/cpuidle/state*/name POLL After the patch: grep . /sys/devices/system/cpu/cpu0/cpuidle/state*/name /sys/devices/system/cpu/cpu0/cpuidle/state0/name:POLL /sys/devices/system/cpu/cpu0/cpuidle/state1/name:C1_ACPI

Fixes: 18734958e9bf ("intel_idle: Use ACPI _CST for processor models without C-state tables") Reported-by: Pengfei Xu pengfei.xu@intel.com Cc: 5.6+ stable@vger.kernel.org # 5.6+ Signed-off-by: Chen Yu yu.c.chen@intel.com

---

drivers/idle/intel_idle.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c index 9a810e4a7946..dbd4be1c271b 100644 --- a/drivers/idle/intel_idle.c +++ b/drivers/idle/intel_idle.c @@ -1236,7 +1236,7 @@ static void __init intel_idle_init_cstates_acpi(struct cpuidle_driver *drv) struct acpi_processor_cx *cx; struct cpuidle_state *state;

•           if (intel_idle_max_cstate_reached(cstate))
  

•           if (intel_idle_max_cstate_reached(cstate - 1))
                    break;
  
            cx = &acpi_state_table.states[cstate];
  

--

Applied as 5.10-rc material with some changelog edits, thanks!