From: Yazen Ghannam <yazen.ghan...@amd.com> AMD systems support the Monitor/Mwait instructions and these can be used for ACPI C1 in the same way as on Intel systems.
Three things are needed: 1) This patch. 2) BIOS that declares a C1 state in _CST to use FFH, with correct values. 3) CPUID_Fn00000005_EDX is non-zero on the system. The BIOS on AMD systems have historically not defined a C1 state in _CST, so the acpi_idle driver uses HALT for ACPI C1. Currently released systems have CPUID_Fn00000005_EDX as reserved/RAZ. If a BIOS is released for these systems that requests a C1 state with FFH, the FFH implementation in Linux will fail since CPUID_Fn00000005_EDX is 0. The acpi_idle driver will then fallback to using HALT for ACPI C1. Future systems are expected to have non-zero CPUID_Fn00000005_EDX and BIOS support for using FFH for ACPI C1. Allow ffh_cstate_init() to succeed on AMD systems. Tested on Fam15h and Fam17h systems. Signed-off-by: Yazen Ghannam <yazen.ghan...@amd.com> --- Link: https://lkml.kernel.org/r/1495030819-4347-1-git-send-email-yazen.ghan...@amd.com v1->v2: * Expand commit message. * Drop change to description string. arch/x86/kernel/acpi/cstate.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/acpi/cstate.c b/arch/x86/kernel/acpi/cstate.c index 8233a63..dde437f 100644 --- a/arch/x86/kernel/acpi/cstate.c +++ b/arch/x86/kernel/acpi/cstate.c @@ -167,7 +167,8 @@ static int __init ffh_cstate_init(void) { struct cpuinfo_x86 *c = &boot_cpu_data; - if (c->x86_vendor != X86_VENDOR_INTEL) + if (c->x86_vendor != X86_VENDOR_INTEL && + c->x86_vendor != X86_VENDOR_AMD) return -1; cpu_cstate_entry = alloc_percpu(struct cstate_entry); -- 2.7.4
