Re: [PATCH] Longhaul - Don't use regs to obtain FSB frequency

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

> On Wed, Dec 13, 2006 at 11:38:18PM +0100, Rafa³ Bilski wrote:
>  > Current code has a problem with FSB on "PowerSaver 1.0" 
>  > CPU. FSB is incorrecly guessed (again) for mini PC by Ebox. 
>  > There is 8x100MHz CPU with "Nehemiah" core. It is reported 
>  > as 8x133MHz. Apparently Longhaul MSR isn't reliable source 
>  > of information if it is RevisionID == 0 for anything else 
>  > then max multiplier. We can't read 200MHz FSB from it nor 
>  > from EBLCR_POWER_ON too. This driver is working only with 
>  > multipliers. FSB frequency is only needed to calculate CPU 
>  > f for Cpufreq core. At boot kernel is calculating processor 
>  > frequency. We know the multiplier. In this way we have bus 
>  > frequency with kHz precision.
> 
> I'm puzzled.  This description talks exclusively about Nehemiah,
> and yet it's making changes to code only run by the pre-Nehemiah cores.
> This makes me especially nervous as those chips don't get a
> great deal of testing any more, and we typically learn that we
> broke them months after making changes.
Well. I don't see a reason for not making this change. It is even more 
compatible with older CPU's, because EBL_CR_POWERON is returning current 
multiplier. And according to Your comments in source it isn't good to 
depend on EBL_CR_POWERON for "PowerSaver" CPU's. Why guess FSB if 
kernel calculated it at boot? In this way it is much simplier. Only 
possible bug is for "PowerSaver" processor running at lower multiplier 
then max.
My point is: can't use EBL_CR_POWERON FSB bits, nor Longhaul MSR FSB bits, 
for "Powersaver" - don't use it at all for any CPU. Find the way that will 
work for all of them.
> Has this been tested on anything other than the system mentioned above?
> It seems like huge potential for regressions here, due to the size
> and impact of the changes.
It has been tested on my Epia M-10000, system mentioned above and two 
Epia SP-13000. I'm currently exchanging e-mails with user who has 
Ezra with "Longhaul ver. 2" connected to SIS630 chipset. Version 2 seems 
to have only max BR bits - same as "Powersaver 1.0". I was planing to use 
same code for V2. I'm not sure yet if Longhaul version 2 can use ACPI C3 
to change frequency.
> 
> 		Dave
Rafa³


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