linux-kernel - Re: [X86] Add recent Centaur CPUs to PAT whitelist

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Message-ID: <20080522170223.GA32314@redhat.com>
Date:	Thu, 22 May 2008 13:02:23 -0400
From:	Dave Jones <davej@...hat.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Yinghai Lu <yhlu.kernel@...il.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [X86] Add recent Centaur CPUs to PAT whitelist

On Thu, May 22, 2008 at 09:48:44AM -0700, H. Peter Anvin wrote:
 > Dave Jones wrote:
 > > On Wed, May 21, 2008 at 04:56:28PM -0700, H. Peter Anvin wrote:
 > >  > Dave Jones wrote:
 > >  > > 
 > >  > > From conversation with Centaur engineers, both the newer generations
 > >  > > of the VIA C7, and their future CPUs support PAT, with no known errata.
 > >  > > 
 > >  > > Signed-off-by: Dave Jones <davej@...hat.com>
 > >  > > 
 > >  > 
 > >  > Question: are there any VIA CPUs that display the PAT CPUID flag that 
 > >  > aren't covered by the above?
 > > 
 > > No.  They only added PAT support with the current Esther (C7) generation iirc.
 > > 
 > 
 > OK, so we should just enable VIA unconditionally as long as PAT is 
 > displayed and not worry about generation numbers; same with Transmeta 
 > (only the Transmeta Efficeon supported PAT, and it had a 
 > strictly-coherent memory system.)

Like so?

Unconditionally enable PAT support on Centaur and Transmeta CPUs.
All known models that advertise PAT have no known errata.

Signed-off-by: Dave Jones <davej@...hat.com>

--- linux-2.6/arch/x86/kernel/cpu/addon_cpuid_features.c~	2008-05-22 12:59:07.000000000 -0400
+++ linux-2.6/arch/x86/kernel/cpu/addon_cpuid_features.c	2008-05-22 12:59:36.000000000 -0400
@@ -62,6 +62,9 @@ void __cpuinit validate_pat_support(stru
 		if (c->x86 == 0xF || (c->x86 == 6 && c->x86_model >= 15))
 			return;
 		break;
+	case X86_VENDOR_CENTAUR:
+	case X86_VENDOR_TRANSMETA:
+		return;
 	}
 
 	pat_disable(cpu_has_pat ?

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