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

From: Simon Horman <[email-masked]>
Date: Fri, 16 Oct 2015 10:48:03 +0900

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

Could I get a review of this from at lest one ppc person?

>  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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