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Subject: Re: [PATCH v2] powerpc xmon: use `dcbf` inplace of `dcbi`
 instruction for 64bit Book3S
From: Balamuruhan S <bala24@linux.ibm.com>
To: Christophe Leroy <christophe.leroy@c-s.fr>, mpe@ellerman.id.au
Date: Sat, 28 Mar 2020 13:33:43 +0530
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On Fri, 2020-03-27 at 16:12 +0100, Christophe Leroy wrote:
> 
> Le 27/03/2020 à 10:03, Balamuruhan S a écrit :
> > On Fri, 2020-03-27 at 07:48 +0100, Christophe Leroy wrote:
> > > Le 26/03/2020 à 07:15, Balamuruhan S a écrit :
> > > > Data Cache Block Invalidate (dcbi) instruction was implemented back in
> > > > PowerPC
> > > > architecture version 2.03. It is obsolete and attempt to use of this
> > > > illegal
> > > > instruction results in a hypervisor emulation assistance interrupt. So,
> > > > ifdef
> > > > it out the option `i` in xmon for 64bit Book3S.
> > > 
> > > I don't understand. You say two contradictory things:
> > > 1/ You say it _was_ added back.
> > > 2/ You say it _is_ obsolete.
> > > 
> > > How can it be obsolete if it was added back ?
> > 
> > I actually learnt it from P8 and P9 User Manual,
> > 
> > The POWER8/POWER9 core does not provide support for the following optional
> > or
> > obsolete instructions (attempted use of these results in a hypervisor
> > emulation
> > assistance interrupt):
> > • tlbia - TLB invalidate all
> > • tlbiex - TLB invalidate entry by index (obsolete)
> > • slbiex - SLB invalidate entry by index (obsolete)
> > • dcba - Data cache block allocate (Book II; obsolete)
> > • dcbi - Data cache block invalidate (obsolete)
> > • rfi - Return from interrupt (32-bit; obsolete)
> > 
> 
> Then that's exactly what you have to say in the coming log.

Sure, I will change the commit log in next version along with your suggested
way to ifdef.

> 
> Maybe you could also change invalidate_dcache_range():
> 
> 	for (i = 0; i < size >> shift; i++, addr += bytes) {
> 		if (IS_ENABLED(CONFIG_PPC_BOOK3S_64))
> 			dcbf(addr);
> 		else
> 			dcbi(addr);
> 	}

I will leave this as is based on the discussion.

Thank you Christophe and Segher.

-- Bala
> 
> 
> 
> 
> Christophe