[PATCH] ARMv7: fix Oprofile events count

[Jean Pihet]

On Mon, 2009-12-14 at 17:58 +0530, Gadiyar, Anand wrote:
> Jean Pihet wrote:
> > 
> > Hi,
> > 
> > Here is a patch that fixes the oprofile events count.
> > If it is OK I will submit it to the patch system.
> > 
> > Any thought?
> > 
> > Regards,
> > Jean
> > 
> > ---
> > ARMv7: fix Oprofile events count
> >     
> >     On Oprofile ARMv7 the PMNC_D bit was set to lower the PMU IRQs
> >     and so to decrease the risk of errata #628216 from appearing.
> >     The effect of setting the PMNC_D bit is that the CCNT counter
> >     is divided by 64, making the program counter events count
> >     inaccurate.
> >     The new OMAP3 r4 cores should have that errata fixed.
> >     
> >     The PMNC_D bit should not be set, this patch fixes it.
> 
> 
> Not an expert, so this is just a general comment.
> 
> Many OMAP3's don't have this newer core, right?
Right. The current OMAP34xx and 35xx do have the problem, so it is
preferable to use oprofile in timer interrupt mode.

> Does it make sense to clear this bit for all ARMv7s?
Yes because the new (i.e. fixed) chips will then use the new code which
is correct.

Those issues have been discussed at length in the past on this very ML.
The conclusion was that the real fix was a HW fix, no suitable SW
workaround could be found. Cf.
http://www.mail-archive.com/linux-omap@vger.kernel.org/msg14084.html

> 
> - Anand
> 
> >     
> >     Signed-off-by: Jean Pihet <jpihet at mvista.com>
> > 
> > diff --git a/arch/arm/oprofile/op_model_v7.c
> > b/arch/arm/oprofile/op_model_v7.c
> > index f20295f..2088a6c 100644
> > --- a/arch/arm/oprofile/op_model_v7.c
> > +++ b/arch/arm/oprofile/op_model_v7.c
> > @@ -191,12 +191,8 @@ int armv7_setup_pmnc(void)
> >                 return -EBUSY;
> >         }
> >  
> > -       /*
> > -        * Initialize & Reset PMNC: C bit, D bit and P bit.
> > -        *  Note: Using a slower count for CCNT (D bit: divide by 64) results
> > -        *   in a more stable system
> > -        */
> > -       armv7_pmnc_write(PMNC_P | PMNC_C | PMNC_D);
> > +       /* Initialize & Reset PMNC: C bit and P bit */
> > +       armv7_pmnc_write(PMNC_P | PMNC_C);
> >  
> >  
> >         for (cnt = CCNT; cnt < CNTMAX; cnt++) {
> > 
> > 
> > 
> >