Subject: Re: powerpc: Add an inline function to update HID0

From: Michael Ellerman <[email-masked]>
Date: Tue, 4 Aug 2015 20:08:58 +1000 (AEST)

On Tue, 2015-04-08 at 08:30:58 UTC, "Gautham R. Shenoy" wrote:
> Section 3.7 of Version 1.2 of the Power8 Processor User's Manual
> prescribes that updates to HID0 be preceded by a SYNC instruction and
> followed by an ISYNC instruction (Page 91).
> 
> Create a function name update_hid0() which follows this recipe and
> invoke it from the static split core path.
> 
> Signed-off-by: Gautham R. Shenoy <[email-masked]>
> ---
>  arch/powerpc/include/asm/kvm_ppc.h       | 11 +++++++++++

Why is it in there? It's not KVM related per se.

Where should it go? I think reg.h would be best, ideally near the definition
for HID0, though that's probably not possible because of ASSEMBLY requirements.
So at the bottom of reg.h ?

> diff --git a/arch/powerpc/include/asm/kvm_ppc.h b/arch/powerpc/include/asm/kvm_ppc.h
> index c6ef05b..325f1d6 100644
> --- a/arch/powerpc/include/asm/kvm_ppc.h
> +++ b/arch/powerpc/include/asm/kvm_ppc.h
> @@ -685,4 +685,15 @@ static inline ulong kvmppc_get_ea_indexed(struct kvm_vcpu *vcpu, int ra, int rb)
>  
>  extern void xics_wake_cpu(int cpu);
>  
> +static inline void update_hid0(unsigned long hid0)
> +{
> +	/*
> +	 *  The HID0 update should at the very least be preceded by a
> +	 *  a SYNC instruction followed by an ISYNC instruction
> +	 */
> +	mb();
> +	mtspr(SPRN_HID0, hid0);
> +	isync();

That's going to turn into three separate inline asm blocks, which is maybe a
bit unfortunate. Have you checked the generated code is what we want, ie. just
sync, mtspr, isync ?

cheers