cpufreq: intel_pstate: Revise global turbo disable check

Setting global turbo flag based on CPU 0 P-state limits is problematic
as it limits max P-state request on every CPU on the system just based
on its P-state limits.

There are two cases in which global.turbo_disabled flag is set:
- When the MSR_IA32_MISC_ENABLE_TURBO_DISABLE bit is set to 1
in the MSR MSR_IA32_MISC_ENABLE. This bit can be only changed by
the system BIOS before power up.
- When the max non turbo P-state is same as max turbo P-state for CPU 0.

The second check is not a valid to decide global turbo state based on
the CPU 0. CPU 0 max turbo P-state can be same as max non turbo P-state,
but for other CPUs this may not be true.

There is no guarantee that max P-state limits are same for every CPU. This
is possible that during fusing max P-state for a CPU is constrained. Also
with the Intel Speed Select performance profile, CPU 0 may not be present
in all profiles. In this case the max non turbo and turbo P-state can be
set to the lowest possible P-state by the hardware when switched to
such profile. Since max non turbo and turbo P-state is same,
global.turbo_disabled flag will be set.

Once global.turbo_disabled is set, any scaling max and min frequency
update for any CPU will result in its max P-state constrained to the max
non turbo P-state.

Hence remove the check of max non turbo P-state equal to max turbo P-state
of CPU 0 to set global turbo disabled flag.

Signed-off-by: Srinivas Pandruvada <[email protected]>
[ rjw: Subject edit ]
Signed-off-by: Rafael J. Wysocki <[email protected]>

Author: spandruvada

drivers/cpufreq/intel_pstate.c

@@ -571,13 +571,9 @@ static void intel_pstate_hybrid_hwp_adjust(struct cpudata *cpu)
 static inline void update_turbo_state(void)
 {
 	u64 misc_en;
-	struct cpudata *cpu;
 
-	cpu = all_cpu_data[0];
 	rdmsrl(MSR_IA32_MISC_ENABLE, misc_en);
-	global.turbo_disabled =
-		(misc_en & MSR_IA32_MISC_ENABLE_TURBO_DISABLE ||
-		 cpu->pstate.max_pstate == cpu->pstate.turbo_pstate);
+	global.turbo_disabled = misc_en & MSR_IA32_MISC_ENABLE_TURBO_DISABLE;
 }
 
 static int min_perf_pct_min(void)