From 2194324d8bbbad1b179c08b6095649b06abd62d5 Mon Sep 17 00:00:00 2001 From: Len Brown Date: Fri, 14 Feb 2014 01:14:13 -0500 Subject: ACPI idle: permit sparse C-state sub-state numbers Linux uses CPUID.MWAIT.EDX to validate the C-states reported by ACPI, silently discarding states which are not supported by the HW. This test is too restrictive, as some HW now uses sparse sub-state numbering, so the sub-state number may be higher than the number of sub-states... Also, rather than silently ignoring an invalid state, we should complain about a firmware bug. In practice... Bay Trail systems originally supported C6-no-shrink as MWAIT sub-state 0x58, and in CPUID.MWAIT.EDX 0x03000000 indicated that there were 3 MWAIT-C6 sub-states. So acpi_idle would discard that C-state because 8 >= 3. Upon discovering this issue, the ucode was updated so that C6-no-shrink was also exported as 0x51, and the BIOS was updated to match. However, systems shipped with 0x58, will never get a BIOS update, and this patch allows Linux to see C6-no-shrink on early Bay Trail. Signed-off-by: Len Brown --- arch/x86/kernel/acpi/cstate.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) (limited to 'arch/x86') diff --git a/arch/x86/kernel/acpi/cstate.c b/arch/x86/kernel/acpi/cstate.c index e69182fd01cf..4b28159e0421 100644 --- a/arch/x86/kernel/acpi/cstate.c +++ b/arch/x86/kernel/acpi/cstate.c @@ -87,7 +87,9 @@ static long acpi_processor_ffh_cstate_probe_cpu(void *_cx) num_cstate_subtype = edx_part & MWAIT_SUBSTATE_MASK; retval = 0; - if (num_cstate_subtype < (cx->address & MWAIT_SUBSTATE_MASK)) { + /* If the HW does not support any sub-states in this C-state */ + if (num_cstate_subtype == 0) { + pr_warn(FW_BUG "ACPI MWAIT C-state 0x%x not supported by HW (0x%x)\n", cx->address, edx_part); retval = -1; goto out; } -- cgit v1.2.3