linux-kernel - Re: [PATCH 6/7] [RFC] enable early TLBs for BG/P

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Message-ID: <1305851941.7481.92.camel@pasglop>
Date:	Fri, 20 May 2011 10:39:01 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Eric Van Hensbergen <ericvh@...il.com>
Cc:	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	bg-linux@...ts.anl-external.org
Subject: Re: [PATCH 6/7] [RFC] enable early TLBs for BG/P

On Wed, 2011-05-18 at 16:24 -0500, Eric Van Hensbergen wrote:
> BG/P maps firmware with an early TLB

That's a bit gross. How often do you call that firmware in practice ?
Aren't you better off instead inserting a TLB entry for it when you call
it instead ? A simple tlbsx. + tlbwe sequence would do. That would free
up a TLB entry for normal use.

Cheers,
Ben.

> Signed-off-by: Eric Van Hensbergen <ericvh@...il.com>
> ---
>  arch/powerpc/include/asm/mmu-44x.h |    6 +++++-
>  1 files changed, 5 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/mmu-44x.h b/arch/powerpc/include/asm/mmu-44x.h
> index ca1b90c..2807d6e 100644
> --- a/arch/powerpc/include/asm/mmu-44x.h
> +++ b/arch/powerpc/include/asm/mmu-44x.h
> @@ -115,8 +115,12 @@ typedef struct {
>  #endif /* !__ASSEMBLY__ */
>  
>  #ifndef CONFIG_PPC_EARLY_DEBUG_44x
> +#ifndef CONFIG_BGP
>  #define PPC44x_EARLY_TLBS	1
> -#else
> +#else /* CONFIG_BGP */
> +#define PPC44x_EARLY_TLBS	2
> +#endif /* CONFIG_BGP */
> +#else /* CONFIG_PPC_EARLY_DEBUG_44x */
>  #define PPC44x_EARLY_TLBS	2
>  #define PPC44x_EARLY_DEBUG_VIRTADDR	(ASM_CONST(0xf0000000) \
>  	| (ASM_CONST(CONFIG_PPC_EARLY_DEBUG_44x_PHYSLOW) & 0xffff))


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