cpu/intel/haswell: Enable timed MWAIT if supported

Broadwell code unconditionally enables timed MWAIT, but not all Haswell
steppings support it. In preparation for merging Haswell and Broadwell,
also enable timed MWAIT on Haswell code, but only if it is supported.

Change-Id: I1d11d62f1801d65ae4d5623994fd55fd35e8f34a
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/46916
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/cpu/intel/haswell/haswell_init.c

@@ -431,7 +431,9 @@ void set_power_limits(u8 power_limit_1_time)
 
 static void configure_c_states(void)
 {
-	msr_t msr;
+	msr_t msr = rdmsr(MSR_PLATFORM_INFO);
+
+	const bool timed_mwait_capable = !!(msr.hi & TIMED_MWAIT_SUPPORTED);
 
 	msr = rdmsr(MSR_PKG_CST_CONFIG_CONTROL);
 	msr.lo |= (1 << 30);	// Package c-state Undemotion Enable
@@ -441,6 +443,10 @@ static void configure_c_states(void)
 	msr.lo |= (1 << 26);	// C1 Auto Demotion Enable
 	msr.lo |= (1 << 25);	// C3 Auto Demotion Enable
 	msr.lo &= ~(1 << 10);	// Disable IO MWAIT redirection
+
+	if (timed_mwait_capable)
+		msr.lo |= (1 << 31);	// Timed MWAIT Enable
+
 	/* The deepest package c-state defaults to factory-configured value. */
 	wrmsr(MSR_PKG_CST_CONFIG_CONTROL, msr);