linux-kernel - Re: What is the best way to identify a new x86 processor that does not implement the CPUID instruction?

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Message-ID: <87tzdv4vqk.fsf@basil.nowhere.org>
Date:	Fri, 08 Aug 2008 13:00:35 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	"David Wilson" <mcs6502@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: What is the best way to identify a new x86 processor that does not implement the CPUID instruction?

"David Wilson" <mcs6502@...il.com> writes:

> I recently bought a Norhtec MicroClient JrSX which uses the Vortex86sx
> System on Chip processor (see http://vortex86sx.com/ for more
> details). This is identified as a Cyrix 486SLC by the Linux kernel due
> to the lack of a CPUID instruction. While this may be seen as a
> cosmetic defect, if the kernel can identify the processor correctly it
> could, for example, use the clock divisor code provided by the
> manufacturer to slow down and speed up the CPU when required.
>
> The question is: how to differentiate this chip from the Cyrix part?
> The freely available "brief data sheet" does not provide much detail.
>
> I have thought of a couple of schemes but am not really keen on either:
>
> 1) Clock speed - the SoC runs at 300+ MHz while the Cyrix part is < 100 MHz
> 2) Look at the PCI VID/PID for the north bridge as this is part of the CPU die.
>
> Does anyone have any suggestions? Thanks.

I would suggest asking the CPU vendor. Surely they have some method.
Then submit a patch to detect that CPU based on that method.

-Andi
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