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

[Andriy Gapon]

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.

-- 
Andriy Gapon