linux-kernel - Re: [git-pull -tip] x86: cpu

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Message-ID: <20090503090908.GA23183@elte.hu>
Date:	Sun, 3 May 2009 11:09:08 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Jaswinder Singh Rajput <jaswinder@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>
Cc:	x86 maintainers <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [git-pull -tip] x86: cpu_debug patches


* Jaswinder Singh Rajput <jaswinder@...nel.org> wrote:

> We can use cpu_has tests for unknown processors but 'cpu model' is 
> accurate and cover all range.
> 
> cpu_has does not cover following registers:
> 1. platform
> 2. poweron
> 3. control
> 4. bios
> 5. freq
> 6. cache
> 7. misc
> 8. base
> 9. ver
> 10. conf

Firstly these should be added to cpufeatures.h.

Then add cpu_has_xxx() accessors need to be added for them and 
during CPU init they have to be properly set, via two methods:

 - via CPUID (where this is possible+specified in docs)
 - or via "later than CPU version X" checks

Your cpu-model table is equivalent to an explicitly enumerated CPU 
version check, but this breaks every time a new CPU comes out. 

"Later than" or CPUID based feature bits are a lot more future-proof 
- we only have to add support for new _features_ (and quirks, 
occasionally), and dont have to maintain that full table of specific 
models to specific features mapping tables.

	Ingo
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