Subject: Re: [PATCH v2 2/3] ppc64: Avoid rfid if no need to clear MSR_LE

From: Sam Mendoza-Jonas <[email-masked]>
Date: Mon, 2 Nov 2015 11:21:43 +1100

On Mon, Nov 02, 2015 at 09:55:53AM +1100, Sam Mendoza-Jonas wrote:
> On Tue, Oct 06, 2015 at 05:55:49PM -0500, Scott Wood wrote:
> > Commit a304e2d82a8c3 ("ppc64: purgatory: Reset primary cpu endian to
> > big-endian) changed bctr to rfid.  rfid is book3s-only and will cause a
> > fatal exception on book3e.
> > 
> > Purgatory is an isolated environment which makes importing information
> > about the subarch awkward, so instead rely on the fact that MSR_LE
> > should never be set on book3e, and the rfid is only needed if MSR_LE is
> > set (and thus needs to be cleared).  In theory that MSR bit is reserved
> > on book3e, rather than zero, but in practice I have not seen it set.
> > 
> > Signed-off-by: Scott Wood <[email-masked]>
> > Cc: Samuel Mendoza-Jonas <[email-masked]>
> > ---
> > v2: new patch
> 
> Looks good to me, thanks for catching this!
> I'll ping Michael too if you'd like his reviewed-by.
> 
> Reviewed-by: Samuel Mendoza-Jonas <[email-masked]>

Following up, also add my

Tested-by: Samuel Mendoza-Jonas <[email-masked]>

> 
> > 
> >  purgatory/arch/ppc64/v2wrap.S | 10 +++++++++-
> >  1 file changed, 9 insertions(+), 1 deletion(-)
> > 
> > diff --git a/purgatory/arch/ppc64/v2wrap.S b/purgatory/arch/ppc64/v2wrap.S
> > index 179ade9..3534080 100644
> > --- a/purgatory/arch/ppc64/v2wrap.S
> > +++ b/purgatory/arch/ppc64/v2wrap.S
> > @@ -116,9 +116,17 @@ master:
> >  	stw	7,0x5c(4)	# and patch it into the kernel
> >  	mr      3,16            # restore dt address
> >  
> > +	mfmsr	5
> > +	andi.	10,5,1		# test MSR_LE
> > +	bne	little_endian
> > +
> > +	li	5,0		# r5 will be 0 for kernel
> > +	mtctr	4		# prepare branch to
> > +	bctr			# start kernel
> > +	
> > +little_endian:			# book3s-only
> >  	mtsrr0	4		# prepare branch to
> >  
> > -	mfmsr	5
> >  	clrrdi	5,5,1		# clear MSR_LE
> >  	mtsrr1	5
> >  
> > -- 
> > 2.1.4
> 
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