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

From: Madhavan Srinivasan <[email-masked]>
Date: Tue, 04 Aug 2015 19:36:00 +0530

On Tuesday 04 August 2015 03:38 PM, Michael Ellerman wrote:
> 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 ?

just to understand, Something like this will not do?

#define update_hid0(x)  __asm__ __volatile__(  
"sync\n"\                      
                                                "mtspr "
__stringify(SPRN_HID0)", %0\n"\
                                                "isync"::"r"(x));

Maddy

>
>> 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
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