linux-kernel - Re: [PATCH 5/5 v2] x86: PAT: make pat_x_mtrr

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Date:	Wed, 18 Jun 2008 17:28:16 +0100 (BST)
From:	Hugh Dickins <hugh@...itas.com>
To:	Andreas Herrmann <andreas.herrmann3@....com>
cc:	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...e.hu>,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>,
	Suresh B Siddha <suresh.b.siddha@...el.com>
Subject: Re: [PATCH 5/5 v2] x86: PAT: make pat_x_mtrr_type() more readable

On Wed, 18 Jun 2008, Andreas Herrmann wrote:
> And the attached patch makes it even shorter.
> (patch against tip/x86/pat -- where your patch is already residing)

Yes, that's delightful, even better, thanks.  After accusing you
of an uninteresting BUG on a fifth value from 2 bits, I had an
inkling that maybe my patch was therefore still stupidly verbose.

> ---
> [PATCH] x86: shrink pat_x_mtrr_type to its essentials
> 
> Signed-off-by: Andreas Herrmann <andreas.herrmann3@....com>

Acked-by: Hugh Dickins <hugh@...itas.com>

> ---
>  arch/x86/mm/pat.c |   30 +++++++++++-------------------
>  1 files changed, 11 insertions(+), 19 deletions(-)
> 
> diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
> index ac3a2b1..227df3c 100644
> --- a/arch/x86/mm/pat.c
> +++ b/arch/x86/mm/pat.c
> @@ -161,29 +161,21 @@ static DEFINE_SPINLOCK(memtype_lock); 	/* protects memtype list */
>   */
>  static unsigned long pat_x_mtrr_type(u64 start, u64 end, unsigned long req_type)
>  {
> -	u8 mtrr_type;
> -
> -	/*
> -	 * We return the PAT request directly for types where PAT takes
> -	 * precedence with respect to MTRR and for UC_MINUS.
> -	 * Consistency checks with other PAT requests is done later
> -	 * while going through memtype list.
> -	 */
> -	if (req_type == _PAGE_CACHE_WC ||
> -	    req_type == _PAGE_CACHE_UC_MINUS ||
> -	    req_type == _PAGE_CACHE_UC)
> -		return req_type;
> -
>  	/*
>  	 * Look for MTRR hint to get the effective type in case where PAT
>  	 * request is for WB.
>  	 */
> -	mtrr_type = mtrr_type_lookup(start, end);
> -	if (mtrr_type == MTRR_TYPE_UNCACHABLE)
> -		return _PAGE_CACHE_UC;
> -	if (mtrr_type == MTRR_TYPE_WRCOMB)
> -		return _PAGE_CACHE_WC;
> -	return _PAGE_CACHE_WB;
> +	if (req_type == _PAGE_CACHE_WB) {
> +		u8 mtrr_type;
> +
> +		mtrr_type = mtrr_type_lookup(start, end);
> +		if (mtrr_type == MTRR_TYPE_UNCACHABLE)
> +			return _PAGE_CACHE_UC;
> +		if (mtrr_type == MTRR_TYPE_WRCOMB)
> +			return _PAGE_CACHE_WC;
> +	}
> +
> +	return req_type;
>  }
>  
>  /*
--
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