intel_idle: Fix max_cstate for processor models without C-state tables

mainline inclusion
from mainline-v5.10-rc2
commit 4e0ba557
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I47H3V
CVE: NA

--------------------------------

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 is incorrect.

Fix this by subtracting 1 from the index when checking max_cstate
in the _CST case.

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: 18734958 ("intel_idle: Use ACPI _CST for processor models without C-state tables")
Reported-by: NPengfei Xu <pengfei.xu@intel.com>
Cc: 5.6+ <stable@vger.kernel.org> # 5.6+
Signed-off-by: NChen Yu <yu.c.chen@intel.com>
[ rjw: Changelog edits ]
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>
Reviewed-by: NHanjun Guo <guohanjun@huawei.com>
Reviewed-by: NXie XiuQi <xiexiuqi@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

drivers/idle/intel_idle.c

@@ -1298,7 +1298,7 @@ static void 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];