Re: [PATCH] Longhaul - Add ignore_latency option

["Rafał Bilski" <rafalbilski@interia.pl>]

>> Some laptops with VIA C3 processor, CLE266 chipset and
>> AMI BIOS have incorrect latency values in FADT table. These
>> laptops seems to be C3 capable, but latency values are to
>> big: 101 for C2 and 1017 for C3. This option will allow
>> user to skip C3 latency test but not C3 address test. AMI
>> BIOS is setting C3 address to correct value in DSDT table.
> 
> This looks very fishy.

So why P_BLK address is valid and have proper lenght?

> 
> C2 latency above 100usec and C3 latency above 1000 usec
> are the official way for the BIOS to tell the OS to NOT USE
> those C-states.  Under no conditions should Linux second
> guess those explicit instructions -- the BIOS may have put
> those values there because you get silent data corruption
> on that particular stepping of the processor or chipset
> if they are enabled.
> 

It is disabled by default.
It is only needed for some laptops.
As far I know there is no data corruption. Chipset and processor 
are exacly the same as on Epia M10000 so I don't expect any.

Why force user to recompilation of distro kernel?

> But the real question is why the longhaul driver is checking
> for C2 and C3 support in the first place -- as they are not
> directly related to the availability of P-states.
> 
> -Len
> 

Because Longhaul isn't using P-states.

Rafa³

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