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Subject: Re: [PATCH 2/6] lib/lzo: enable 64-bit CTZ on Arm
To:     Christoph Hellwig <hch@infradead.org>,
        Dave Rodgman <dave.rodgman@arm.com>
References: <20181121115922.22864-2-dave.rodgman@arm.com>
 <20181121115922.22864-3-dave.rodgman@arm.com>
 <20181121173114.GA14352@infradead.org>
Cc:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        nd <nd@arm.com>,
        "herbert@gondor.apana.org.au" <herbert@gondor.apana.org.au>,
        "davem@davemloft.net" <davem@davemloft.net>,
        Matt Sealey <Matt.Sealey@arm.com>,
        "nitingupta910@gmail.com" <nitingupta910@gmail.com>,
        "rpurdie@openedhand.com" <rpurdie@openedhand.com>,
        "minchan@kernel.org" <minchan@kernel.org>,
        "sergey.senozhatsky.work@gmail.com" 
        <sergey.senozhatsky.work@gmail.com>
From:   "Markus F.X.J. Oberhumer" <markus@oberhumer.com>
Organization: oberhumer.com
Message-ID: <5BF61D27.5000002@oberhumer.com>
Date:   Thu, 22 Nov 2018 04:06:15 +0100
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On 2018-11-21 18:31, Christoph Hellwig wrote:
>>  #define LZO_USE_CTZ32	1
>>  #elif defined(__i386__) || defined(__powerpc__)
>>  #define LZO_USE_CTZ32	1
>> -#elif defined(__arm__) && (__LINUX_ARM_ARCH__ >= 5)
>> +#elif defined(__arm__)
>> +#if (__LINUX_ARM_ARCH__ >= 5)
>>  #define LZO_USE_CTZ32	1
>>  #endif
>> +#if (__LINUX_ARM_ARCH__ >= 6) && (CONFIG_THUMB2_KERNEL)
>> +#define LZO_USE_CTZ64	1
> 
> All of this really needs to be driven by Kconfig symbols that
> the architecture selects instead of magic arch ifdefs here.

LZO_USE_CTZ32 and LZO_USE_CTZ64 should only be defined if there
is a *fast* hardware instruction.

It would be nice if there exists a kernel #define we could
use for detecting that.

-- 
Markus Oberhumer, <markus@oberhumer.com>, http://www.oberhumer.com/