linux-kernel - Re: [PATCH V9 03/13] MIPS: Loongson: Introduce and use cpu_has_coherent

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Message-ID: <5166ED66.7020307@realitydiluted.com>
Date:	Thu, 11 Apr 2013 12:05:42 -0500
From:	"Steven J. Hill" <sjhill@...litydiluted.com>
To:	Huacai Chen <chenhc@...ote.com>
CC:	Ralf Baechle <ralf@...ux-mips.org>, linux-mips@...ux-mips.org,
	linux-kernel@...r.kernel.org, Fuxin Zhang <zhangfx@...ote.com>,
	Zhangjin Wu <wuzhangjin@...il.com>,
	Hongliang Tao <taohl@...ote.com>, Hua Yan <yanh@...ote.com>
Subject: Re: [PATCH V9 03/13] MIPS: Loongson: Introduce and use cpu_has_coherent_cache
 feature

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On 01/30/2013 12:24 AM, Huacai Chen wrote:
> Loongson-3 maintains cache coherency by hardware. So we introduce a cpu 
> feature named cpu_has_coherent_cache and use it to modify MIPS's cache 
> flushing functions.
> 
> Signed-off-by: Huacai Chen <chenhc@...ote.com> Signed-off-by: Hongliang Tao
> <taohl@...ote.com> Signed-off-by: Hua Yan <yanh@...ote.com> --- 
> arch/mips/include/asm/cacheflush.h                 |    6 +++++ 
> arch/mips/include/asm/cpu-features.h               |    3 ++ 
> .../asm/mach-loongson/cpu-feature-overrides.h      |    6 +++++ 
> arch/mips/mm/c-r4k.c                               |   21
> ++++++++++++++++++- 4 files changed, 34 insertions(+), 2 deletions(-)
> 
Hello.

This patch masks the problem that you are not properly probing your L1 caches
to start with. For some reason in 'probe_pcache()' you reach the default case
where the primary data cache is marked as having aliases. If your CPU truly is
HW coherent with no aliases, then MIPS_CACHE_ALIASES should never get set.
Fixing this would eliminate the 'arch/mips/include/asm/cacheflush.h' and
'arch/mips/mm/c-r4k.c' changes completely. There is no need to add more CPU
feature bits for this single platform, thus changes to 'cpu-features.h' and
'cpu-features-overrides.h' will not be accepted.

Also, please do not copy the <linux-kernel@...r.kernel.org> mailing list
unless your patch touches files outside of 'arch/mips' in order to cut down
traffic on an already busy list. Thanks.

Steve
- -----
<sjhill@...s.com>
<Steven.Hill@...tec.com>
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