Re: [Xen-devel] [PATCH]ACPI: re-enable mwait for xen cpuidle

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

On 04/02/2010 09:27 AM, Wei, Gang wrote:
> Updated the 2nd patch, only set MWAIT feature for dom0.
>
> Jimmy
>
> ACPI: re-enable mwait for xen cpuidle
>
> Xen hypervisor doesn't export mwait feature to dom0, but latest Linux kernel 
> start to check this feature while initializing _PDC object. Modify xen_cpuid to 
> re-enable mwait for xen cpuidle.
>    
What if the CPU really doesn't have MWAIT?

But I agree with your original assessment that setting MWAIT just to get 
a couple of paths in ACPI parsing enabled is probably overkill, but I 
don't like the idea of putting xen-specific tests into the acpi code.
Would it be possible to change the parser code to parse unconditionally 
and then ignore the MWAIT-specific stuff later on?  (I haven't looked at 
the structure of the code, so I'm not sure if this suggestion even makes 
sense.)
    J

> Signed-off-by: Wei Gang<gang.wei@xxxxxxxxx>
>
> diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
> index c3e8bff..82f3826 100644
> --- a/arch/x86/xen/enlighten.c
> +++ b/arch/x86/xen/enlighten.c
> @@ -182,6 +182,9 @@ static void __init xen_banner(void)
>   static __read_mostly unsigned int cpuid_leaf1_edx_mask = ~0;
>   static __read_mostly unsigned int cpuid_leaf1_ecx_mask = ~0;
>   static __read_mostly unsigned int cpuid_leaf81_edx_mask = ~0;
> +static __read_mostly unsigned int cpuid_leaf1_ecx_set;
> +static __read_mostly unsigned int cpuid_leaf5_ecx_set;
> +static __read_mostly unsigned int cpuid_leaf5_edx_set;
>
>   static void xen_cpuid(unsigned int *ax, unsigned int *bx,
>                       unsigned int *cx, unsigned int *dx)
> @@ -189,6 +192,8 @@ static void xen_cpuid(unsigned int *ax, unsigned int *bx,
>         unsigned maskebx = ~0;
>         unsigned maskecx = ~0;
>         unsigned maskedx = ~0;
> +       unsigned setecx  =  0;
> +       unsigned setedx  =  0;
>
>         /*
>          * Mask out inconvenient features, to try and disable as many
> @@ -198,6 +203,12 @@ static void xen_cpuid(unsigned int *ax, unsigned int *bx,
>         case 0x1:
>                 maskecx = cpuid_leaf1_ecx_mask;
>                 maskedx = cpuid_leaf1_edx_mask;
> +               setecx  = cpuid_leaf1_ecx_set;
> +               break;
> +
> +       case 0x5: /* MWAIT INFO */
> +               setecx = cpuid_leaf5_ecx_set;
> +               setedx = cpuid_leaf5_edx_set;
>                 break;
>
>         case 0xb:
> @@ -220,6 +231,8 @@ static void xen_cpuid(unsigned int *ax, unsigned int *bx,
>         *bx&= maskebx;
>         *cx&= maskecx;
>         *dx&= maskedx;
> +       *cx |= setecx;
> +       *dx |= setedx;
>   }
>
>   static __init void xen_init_cpuid_mask(void)
> @@ -238,6 +251,11 @@ static __init void xen_init_cpuid_mask(void)
>                           (1<<  X86_FEATURE_MCA)  |  /* disable MCA */
>                           (1<<  X86_FEATURE_APIC) |  /* disable local APIC */
>                           (1<<  X86_FEATURE_ACPI));  /* disable ACPI */
> +       else {
> +               cpuid_leaf1_ecx_set = 1<<  (X86_FEATURE_MWAIT % 32);
> +               cpuid_leaf5_ecx_set = 0x3; /* EXTENSIONS_SUPPORTED | 
> INTERRUPT_BREAK */
> +               cpuid_leaf5_edx_set = ~0;
> +       }
>
>         ax = 1;
>         cx = 0;
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