ACPI: allow C3 > 1000usec
Len Brown [Wed, 20 Jan 2010 04:10:04 +0000 (23:10 -0500)]
Do for C3 what the previous patch did for C2.

The C2 patch was in response to a highly visible
and multiply reported C-state/turbo failure,
while this change has no bug report in-hand.

This will enable C3 in Linux on systems where BIOS
overstates C3 latency in _CST.  It will also enable
future systems which may actually have C3 > 1000usec.

Linux has always ignored ACPI BIOS C3 with exit latency > 1000 usec,
and the ACPI spec is clear that is correct FADT-supplied C3.

However, the ACPI spec explicitly states that _CST-supplied C-states
have no latency limits.

So move the 1000usec C3 test out of the code shared
by FADT and _CST code-paths, and into the FADT-specific path.

Signed-off-by: Len Brown <len.brown@intel.com>

drivers/acpi/processor_idle.c

index 8f6da9a..2c543b4 100644 (file)
@@ -316,6 +316,17 @@ static int acpi_processor_get_power_info_fadt(struct acpi_processor *pr)
                pr->power.states[ACPI_STATE_C2].address = 0;
        }
 
+       /*
+        * FADT supplied C3 latency must be less than or equal to
+        * 1000 microseconds.
+        */
+       if (acpi_gbl_FADT.C3latency > ACPI_PROCESSOR_MAX_C3_LATENCY) {
+               ACPI_DEBUG_PRINT((ACPI_DB_INFO,
+                       "C3 latency too large [%d]\n", acpi_gbl_FADT.C3latency));
+               /* invalidate C3 */
+               pr->power.states[ACPI_STATE_C3].address = 0;
+       }
+
        ACPI_DEBUG_PRINT((ACPI_DB_INFO,
                          "lvl2[0x%08x] lvl3[0x%08x]\n",
                          pr->power.states[ACPI_STATE_C2].address,
@@ -533,16 +544,6 @@ static void acpi_processor_power_verify_c3(struct acpi_processor *pr,
                return;
 
        /*
-        * C3 latency must be less than or equal to 1000
-        * microseconds.
-        */
-       else if (cx->latency > ACPI_PROCESSOR_MAX_C3_LATENCY) {
-               ACPI_DEBUG_PRINT((ACPI_DB_INFO,
-                                 "latency too large [%d]\n", cx->latency));
-               return;
-       }
-
-       /*
         * PIIX4 Erratum #18: We don't support C3 when Type-F (fast)
         * DMA transfers are used by any ISA device to avoid livelock.
         * Note that we could disable Type-F DMA (as recommended by