Login | Register For Free | Help
Search for: (Advanced)

Mailing List Archive: Linux: Kernel
Re: 2.6.14: CR4 not needed to be inspected on the 486 anymore?
 

Index | Next | Previous | View Flat


zach at vmware

Nov 3, 2005, 3:49 PM


Views: 643
Permalink
Re: 2.6.14: CR4 not needed to be inspected on the 486 anymore? [In reply to]

Maciej W. Rozycki wrote:

>On Thu, 3 Nov 2005, Zachary Amsden wrote:
>
>
>
>>>disables code to retrieve the actual value of CR4 on 486-class systems
>>>(which may or may not implement the register, depending on the exact CPU
>>>type and stepping). This seems suspicious to me, but I have to admit I
>>>haven't followed the discussion on the issue if there was any.
>>>
>>>
>>>
>>>
>>This was deliberate. CR4 doesn't exist on standard 486 class systems,
>>and I'm not sure how you could make use of it anyway, since the features
>>used by Linux - machine check, page size extensions, time stamp counter,
>>global pages, are only available in Pentium and later class systems, and
>>identified by CPUID, which also doesn't exist on 486.
>>
>>
>
> Later Intel i486DX2 and i486DX4 processors (the so called "write-back
>enhanced" ones) did support page size extensions (4MB pages) and as far as
>I know we do use them on such chips. They did implement the CPUID
>instruction, too (as well as late i486SX and i486SX2 chips that did not
>support PSE). That's a counter-example that proves the actual value of
>CR4 is going to be useful on these systems. These chips also implemented
>the VME feature (the PVI and VME bits of CR4), but they may not be
>terribly useful for us.
>
> I used quite a few of such chips myself in mid 90s -- you may search
>archives of various mailing lists for examples of "cpuinfo" dumps for such
>processors.
>

Finally got the relevant information from Intel. The embedded i486DX-2/4
series does support CPUID, and PSE, and thus CR4. Ugh. Also just found
this guy:

$ cat /proc/cpuinfo
processor : 0
vendor_id : GenuineIntel
cpu family : 4
model : 7
model name : 486 DX/2-WB
stepping : 0
fdiv_bug : no
hlt_bug : no
f00f_bug : no
coma_bug : no
fpu : yes
fpu_exception : yes
cpuid level : 1
wp : yes
flags : fpu vme pse
bogomips : 32.25


He won't like me too much. I'll write up a proper patch for this, a la
mode de rdmsr_safe / wrmsr_safe. At least it's not a bug, just missing
information.

Zach
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo [at] vger
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

Subject User Time
2.6.14: CR4 not needed to be inspected on the 486 anymore? macro at linux-mips Nov 3, 2005, 8:12 AM
    Re: 2.6.14: CR4 not needed to be inspected on the 486 anymore? zach at vmware Nov 3, 2005, 8:34 AM
        Re: 2.6.14: CR4 not needed to be inspected on the 486 anymore? macro at linux-mips Nov 3, 2005, 9:20 AM
    Re: 2.6.14: CR4 not needed to be inspected on the 486 anymore? zach at vmware Nov 3, 2005, 3:49 PM
        Re: 2.6.14: CR4 not needed to be inspected on the 486 anymore? ak at suse Nov 5, 2005, 9:40 AM
            Re: 2.6.14: CR4 not needed to be inspected on the 486 anymore? macro at linux-mips Nov 7, 2005, 1:38 AM
    Re: 2.6.14: CR4 not needed to be inspected on the 486 anymore? zach at vmware Nov 7, 2005, 7:44 AM
        Re: 2.6.14: CR4 not needed to be inspected on the 486 anymore? macro at linux-mips Nov 7, 2005, 8:37 AM
    Re: 2.6.14: CR4 not needed to be inspected on the 486 anymore? zach at vmware Nov 7, 2005, 8:51 AM
        Re: 2.6.14: CR4 not needed to be inspected on the 486 anymore? linux-os at analogic Nov 7, 2005, 9:00 AM
        Re: 2.6.14: CR4 not needed to be inspected on the 486 anymore? macro at linux-mips Nov 7, 2005, 9:11 AM
    Re: 2.6.14: CR4 not needed to be inspected on the 486 anymore? zach at vmware Nov 7, 2005, 9:32 AM
        Re: 2.6.14: CR4 not needed to be inspected on the 486 anymore? linux-os at analogic Nov 7, 2005, 10:17 AM
    Re: 2.6.14: CR4 not needed to be inspected on the 486 anymore? linux at rainbow-software Nov 7, 2005, 11:02 AM

  Index | Next | Previous | View Flat
 
 


Interested in having your list archived? Contact Gossamer Threads
 
  Web Applications & Managed Hosting Powered by Gossamer Threads Inc.