diff options
| author | Len Brown <len.brown@intel.com> | 2014-02-14 01:14:13 -0500 |
|---|---|---|
| committer | Len Brown <len.brown@intel.com> | 2014-02-19 17:33:18 -0500 |
| commit | 2194324d8bbbad1b179c08b6095649b06abd62d5 (patch) | |
| tree | ba4ecb67ef1acf13b2426356d0abe1db5f52188a /arch/x86/kernel/acpi/cstate.c | |
| parent | b28a960c42fcd9cfc987441fa6d1c1a471f0f9ed (diff) | |
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 <len.brown@intel.com>
Diffstat (limited to 'arch/x86/kernel/acpi/cstate.c')
| -rw-r--r-- | arch/x86/kernel/acpi/cstate.c | 4 |
1 files changed, 3 insertions, 1 deletions
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; } |