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Commit 09fd4b4e authored by Thomas Gleixner's avatar Thomas Gleixner Committed by Ingo Molnar
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x86: use cpuid to check MWAIT support for C1 



cpuid(0x05) provides extended information about MWAIT in EDX when bit
0 of ECX is set. Bit 4-7 of EDX determine whether MWAIT is supported
for C1. C1E enabled CPUs have these bits set to 0.

Based on an earlier patch from Andi Kleen.

Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 732d7be1

arch/x86/kernel/process.c

+20 −8
Original line number Original line Diff line number Diff line
@@ -122,19 +122,31 @@ static void poll_idle(void) 
 *

 *

 * idle=mwait overrides this decision and forces the usage of mwait.

 * idle=mwait overrides this decision and forces the usage of mwait.

 */

 */



#define MWAIT_INFO			0x05

#define MWAIT_ECX_EXTENDED_INFO		0x01

#define MWAIT_EDX_C1			0xf0



static int __cpuinit mwait_usable(const struct cpuinfo_x86 *c)

static int __cpuinit mwait_usable(const struct cpuinfo_x86 *c)

{

{

	u32 eax, ebx, ecx, edx;



	if (force_mwait)

	if (force_mwait)

		return 1;

		return 1;





	if (c->x86_vendor == X86_VENDOR_AMD) {

	if (c->cpuid_level < MWAIT_INFO)

		switch(c->x86) {

		case 0x10:

		case 0x11:

		return 0;

		return 0;

		}



	}

	cpuid(MWAIT_INFO, &eax, &ebx, &ecx, &edx);

	/* Check, whether EDX has extended info about MWAIT */

	if (!(ecx & MWAIT_ECX_EXTENDED_INFO))

		return 1;

		return 1;



	/*

	 * edx enumeratios MONITOR/MWAIT extensions. Check, whether

	 * C1  supports MWAIT

	 */

	return (edx & MWAIT_EDX_C1);

}

}





void __cpuinit select_idle_routine(const struct cpuinfo_x86 *c)

void __cpuinit select_idle_routine(const struct cpuinfo_x86 *c)