linux-kernel - Re: i686 quirk for AMD Geode

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Message-ID: <20091108134759.51ca97fc@mycelium.queued.net>
Date:	Sun, 8 Nov 2009 13:47:59 -0500
From:	Andres Salomon <dilinger@...labora.co.uk>
To:	Matteo Croce <technoboy85@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: i686 quirk for AMD Geode

On Sun, 8 Nov 2009 19:22:47 +0100
Matteo Croce <technoboy85@...il.com> wrote:

> On Sun, Nov 8, 2009 at 5:05 PM, Andres Salomon
> <dilinger@...labora.co.uk> wrote:
> > See comment below.  BTW, how does this affect performance on LXs?
> > Do you have any hard numbers for common tasks?
> >
> > On Sat, 7 Nov 2009 12:11:55 +0100
> > Matteo Croce <technoboy85@...il.com> wrote:
> > [...]
> >>
> >> --- a/arch/x86/kernel/Makefile        2009-11-06 15:06:52.246223989
> >> +0100 +++ b/arch/x86/kernel/Makefile  2009-11-06
> >> 15:07:04.294054613 +0100 @@ -89,7 +89,7 @@
> >>  obj-$(CONFIG_HPET_TIMER)     += hpet.o
> >>
> >>  obj-$(CONFIG_K8_NB)          += k8.o
> >> -obj-$(CONFIG_MGEODE_LX)              += geode_32.o mfgpt_32.o
> >> +obj-$(CONFIG_MGEODE_LX)              += geode_32.o mfgpt_32.o
> >> nopl_emu.o obj-$(CONFIG_DEBUG_RODATA_TEST)    += test_rodata.o
> >>  obj-$(CONFIG_DEBUG_NX_TEST)  += test_nx.o
> >>
> >> --- a/arch/x86/kernel/cpu/amd.c       2009-11-06 15:06:52.254223805
> >> +0100 +++ b/arch/x86/kernel/cpu/amd.c 2009-11-06
> >> 15:07:04.294054613 +0100 @@ -138,8 +138,10 @@
> >>       }
> >>
> >>       if (c->x86_model == 10) {
> >> -             /* AMD Geode LX is model 10 */
> >> -             /* placeholder for any needed mods */
> >> +             /* Geode only lacks the NOPL instruction to be i686,
> >> +                but we can emulate it in the exception handler
> >> +                and promote it to a class 6 cpu */
> >> +             boot_cpu_data.x86 = 6;
> >>               return;
> >>       }
> >
> > If you're going to update this, you also need to make sure that
> > you're not breaking things that check it.  For example,
> > arch/x86/include/asm/geode.h has an is_geode_lx check that expects
> > boot_cpu_data.x86 to be 5.  Please be sure to update all these
> > places when creating a patch like this.
> >
> 
> Right, but what if is_geode_lx() is called befor the x86.id change
> takes effect? Maybe something like this?
> 
> --- a/arch/x86/include/asm/geode.h 2009-11-08 19:13:43.531117343 +0100
> +++ b/arch/x86/include/asm/geode.h      2009-11-08 19:19:42.130618023
> +0100 @@ -177,7 +177,7 @@
>  static inline int is_geode_lx(void)
>  {
>         return ((boot_cpu_data.x86_vendor == X86_VENDOR_AMD) &&
> -               (boot_cpu_data.x86 == 5) &&
> +               (boot_cpu_data.x86 == 5 || boot_cpu_data.x86 == 6) &&
>                 (boot_cpu_data.x86_model == 10));
>  }


Yeah, that looks better.
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