From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <mikey@neuling.org>
From: Michael Neuling <mikey@neuling.org>
To: Michael Ellerman <michael@ellerman.id.au>
Subject: Re: [PATCH V3 1/5] powerpc,
 perf: Add new BHRB related instructions for POWER8
In-reply-to: <20130421234109.GC22246@concordia>
References: <1366287976-3900-1-git-send-email-khandual@linux.vnet.ibm.com>
 <1366287976-3900-2-git-send-email-khandual@linux.vnet.ibm.com>
 <20130421234109.GC22246@concordia>
Date: Mon, 22 Apr 2013 11:13:43 +1000
Message-ID: <14010.1366593223@ale.ozlabs.ibm.com>
Cc: linuxppc-dev@ozlabs.org, linux-kernel@vger.kernel.org,
 Anshuman Khandual <khandual@linux.vnet.ibm.com>
List-Id: Linux on PowerPC Developers Mail List <linuxppc-dev.lists.ozlabs.org>
List-Unsubscribe: <https://lists.ozlabs.org/options/linuxppc-dev>,
 <mailto:linuxppc-dev-request@lists.ozlabs.org?subject=unsubscribe>
List-Archive: <http://lists.ozlabs.org/pipermail/linuxppc-dev/>
List-Post: <mailto:linuxppc-dev@lists.ozlabs.org>
List-Help: <mailto:linuxppc-dev-request@lists.ozlabs.org?subject=help>
List-Subscribe: <https://lists.ozlabs.org/listinfo/linuxppc-dev>,
 <mailto:linuxppc-dev-request@lists.ozlabs.org?subject=subscribe>

Michael Ellerman <michael@ellerman.id.au> wrote:

> On Thu, Apr 18, 2013 at 05:56:12PM +0530, Anshuman Khandual wrote:
> > This patch adds new POWER8 instruction encoding for reading
> > the BHRB buffer entries and also clearing it. Encoding for
> > "clrbhrb" instruction is straight forward.
> 
> Which is "clear branch history rolling buffer" ?
> 
> > But "mfbhrbe"
> > encoding involves reading a certain index of BHRB buffer
> > into a particular GPR register.
> 
> And "Move from branch history rolling buffer entry" ?
> 
> > diff --git a/arch/powerpc/include/asm/ppc-opcode.h b/arch/powerpc/include/asm/ppc-opcode.h
> > index 8752bc8..93ae5a1 100644
> > --- a/arch/powerpc/include/asm/ppc-opcode.h
> > +++ b/arch/powerpc/include/asm/ppc-opcode.h
> > @@ -82,6 +82,7 @@
> >  #define	__REGA0_R31	31
> >  
> >  /* sorted alphabetically */
> > +#define PPC_INST_BHRBE			0x7c00025c
> 
> I don't think you really need this, just use the literal value below.

The rest of the defines in this file do this, so Anshuman's right. 

> > @@ -297,6 +298,12 @@
> >  #define PPC_NAP			stringify_in_c(.long PPC_INST_NAP)
> >  #define PPC_SLEEP		stringify_in_c(.long PPC_INST_SLEEP)
> >  
> > +/* BHRB instructions */
> > +#define PPC_CLRBHRB		stringify_in_c(.long 0x7c00035c)
> > +#define PPC_MFBHRBE(r, n)	stringify_in_c(.long PPC_INST_BHRBE | \
> > +						__PPC_RS(r) | \
> > +							(((n) & 0x1f) << 11))
> 
> Why are you not using ___PPC_RB(n) here ?

Actually, this is wrong.  The number field should be 10 bits (0x3ff),
not 5 (0x1f)  Anshuman please fix.  

Mikey