linux-kernel - Re: i686 quirk for AMD Geode

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Message-ID: <40101cc30911081022h33ac20d7od591a9bcdb739f04@mail.gmail.com>
Date:	Sun, 8 Nov 2009 19:22:47 +0100
From:	Matteo Croce <technoboy85@...il.com>
To:	Andres Salomon <dilinger@...labora.co.uk>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: i686 quirk for AMD Geode

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));
 }
--
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