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From: Sreekanth Reddy <sreekanth.reddy@broadcom.com>
Date: Fri, 21 Apr 2017 13:26:29 +0530
Message-ID: <CAK=zhgpmcmq-CnWuU9=WRJpAaEduw63LSPLE9yZzF_sUHkM4AA@mail.gmail.com>
Subject: Re: [PATCH V2] scsi: mpt3sas: remove redundant wmb
To: "Martin K. Petersen" <martin.petersen@oracle.com>
Cc: Sinan Kaya <okaya@codeaurora.org>,
        "linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>,
        timur@codeaurora.org, linux-arm-msm@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        Sathya Prakash <sathya.prakash@broadcom.com>,
        Chaitra P B <chaitra.basappa@broadcom.com>,
        Suganath Prabu Subramani 
        <suganath-prabu.subramani@broadcom.com>,
        "James E.J. Bottomley" <jejb@linux.vnet.ibm.com>,
        "open list:LSILOGIC MPT FUSION DRIVERS (FC/SAS/SPI)" 
        <MPT-FusionLinux.pdl@broadcom.com>,
        open list <linux-kernel@vger.kernel.org>
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On Thu, Apr 20, 2017 at 7:58 AM, Martin K. Petersen
<martin.petersen@oracle.com> wrote:
> Sinan Kaya <okaya@codeaurora.org> writes:
>
>> Due to relaxed ordering requirements on multiple architectures,
>> drivers are required to use wmb/rmb/mb combinations when they need to
>> guarantee observability between the memory and the HW.
>>
>> The mpt3sas driver is already using wmb() for this purpose.  However,
>> it issues a writel following wmb(). writel() function on arm/arm64
>> arhictectures have an embedded wmb() call inside.

[Sreekanth] Whether same thing applicable for SPARC & POWER
architectures. If yes then we are fine with this patch changes.

>>
>> This results in unnecessary performance loss and code duplication.
>>
>> writel already guarantees ordering for both cpu and bus. we don't need
>> additional wmb()
>
> Broadcom folks, please review!
>
> --
> Martin K. Petersen      Oracle Linux Engineering