Hi Aneesh,

On Mon,  9 Jul 2012 18:43:33 +0530 "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com> wrote:
>
> diff --git a/arch/powerpc/include/asm/mmu-hash64.h b/arch/powerpc/include/asm/mmu-hash64.h
> index 1c65a59..1c984a6 100644
> --- a/arch/powerpc/include/asm/mmu-hash64.h
> +++ b/arch/powerpc/include/asm/mmu-hash64.h
> @@ -154,9 +155,25 @@ struct mmu_psize_def
>  #define MMU_SEGSIZE_256M	0
>  #define MMU_SEGSIZE_1T		1
>  
> +/*
> + * encode page number shift.
> + * Inorder to fit the 78 bit va in a 64 bit variable we shift the va by
> + * 12 bits. This enable us to address upto 76 bit va.
> + * For hpt hash from a va we can ignore the page size bits of va and for
> + * hpte encoding we ignore upto 23 bits of va. So ignoring lower 12 bits ensure
> + * we work in all cases including 4k page size.
> + */
> +#define VPN_SHIFT	12
>  
> +static inline unsigned long hpte_encode_avpn(unsigned long vpn, int psize,
> +					     int ssize)
> +{
> +	unsigned long v;
> +	/*
> +	 * The AVA field omits the low-order 23 bits of the 78 bits VA.
> +	 * These bits are not needed in the PTE, because the
> +	 * low-order b of these bits are part of the byte offset
> +	 * into the virtual page and, if b < 23, the high-order
> +	 * 23-b of these bits are always used in selecting the
> +	 * PTEGs to be searched
> +	 */
> +	BUG_ON(VPN_SHIFT > 23);

Could/should this be BUILD_BUG_ON()?

-- 
Cheers,
Stephen Rothwell                    sfr@canb.auug.org.au