kern/108581: [sysctl] sysctl: hw.acpi.cpu.cx_lowest: Invalid argument

[Stephane E. Potvin]

Andriy Gapon wrote:
> on 26/03/2009 17:10 Bruce Cran said the following:
>> On Thu, 26 Mar 2009 17:04:19 +0200
>> Andriy Gapon <avg at icyb.net.ua> wrote:
>>
>>> on 26/03/2009 16:41 Bruce Cran said the following:
>>>> I added lots of printfs to acpi_cpu.c and found that it's occuring
>>>> in acpi_cpu_startup; initializing it to 3 in that function (which I
>>>> wrongly assumed was the lowest Cx state supported in ACPI) fixed
>>>> the problem on my Athlon XP PC because the generic cx handling code
>>>> then lowered cpu_cx_count to 1 based on the fact that
>>>> sc->cpu_cx_count was also 1.
>>>>
>>> Ok, yes, the real issue is in acpi_cpu_generic_cx_probe, namely in
>>> early exits from it. So,  sc->cpu_cx_count is always set to at least
>>> 1, but if we exit via one of the returns before the end of function,
>>> then global cpu_cx_count is never updated.
>>>
>> Exactly:
>>
>> acpi: acpi_cpu_startup: initializing cpu_cx_count to 0
>> acpi_cpu_generic_cx_probe
>> if sc->cpu_p_blk_len < 5  [sc->cpu_p_blk_len = 0]
>> acpi: acpi_cpu_startup: cpu 0,cpu_cx_count = 0,sc->cpu_cx_count = 1
>>
>> So we're hitting an early exit in acpi_cpu_generic_cx_probe.
>>
> 
> John, what would be a better fix - initialize the global variable to 1 or use goto
> in acpi_cpu_generic_cx_probe?
> I think the latter is more consistent and obvious, the former is simpler and
> safer, though.
> 

Your right, it seems that I need to order some more pointy hats. There
should have been a goto there to jump at the end in order to initialize
the global cpu_cx_count. The following patch should fix your issue.
John, is this ok with you?

Index: acpi_cpu.c
===================================================================
--- acpi_cpu.c	(revision 190318)
+++ acpi_cpu.c	(working copy)
@@ -576,7 +576,7 @@
      * "only" C1-C3 is not a hardship.
      */
     if (sc->cpu_p_blk_len < 5)
-	return;
+	goto done;

     /* Validate and allocate resources for C2 (P_LVL2). */
     gas.SpaceId = ACPI_ADR_SPACE_SYSTEM_IO;
@@ -594,7 +594,7 @@
 	}
     }
     if (sc->cpu_p_blk_len < 6)
-	return;
+	goto done;

     /* Validate and allocate resources for C3 (P_LVL3). */
     if (AcpiGbl_FADT.C3Latency <= 1000 && !(cpu_quirks &
CPU_QUIRK_NO_C3)) {
@@ -610,6 +610,7 @@
 	}
     }

+done:
     /* Update the largest cx_count seen so far */
     if (sc->cpu_cx_count > cpu_cx_count)
 	cpu_cx_count = sc->cpu_cx_count;