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Subject: Re: [PATCH] alpha: io: reorder barriers to guarantee writeX() and
 iowriteX() ordering #2
To:     linux-alpha@vger.kernel.org, arnd@arndb.de, timur@codeaurora.org,
        sulrich@codeaurora.org, Matt Turner <mattst88@gmail.com>
Cc:     linux-arm-msm@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        Richard Henderson <rth@twiddle.net>,
        Ivan Kokshaysky <ink@jurassic.park.msu.ru>,
        Philippe Ombredanne <pombredanne@nexb.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Kate Stewart <kstewart@linuxfoundation.org>,
        linux-kernel@vger.kernel.org
References: <1523917017-28084-1-git-send-email-okaya@codeaurora.org>
 <b9d845ad-62af-d300-53d9-2b62f5da6c44@codeaurora.org>
From:   Sinan Kaya <okaya@codeaurora.org>
Message-ID: <2fd54f7c-ff73-5935-a253-c924f4373cc6@codeaurora.org>
Date:   Fri, 20 Apr 2018 12:20:11 -0400
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Hi Matt,

On 4/17/2018 2:43 PM, Sinan Kaya wrote:
> On 4/16/2018 6:16 PM, Sinan Kaya wrote:
>> memory-barriers.txt has been updated with the following requirement.
>>
>> "When using writel(), a prior wmb() is not needed to guarantee that the
>> cache coherent memory writes have completed before writing to the MMIO
>> region."
>>
>> Current writeX() and iowriteX() implementations on alpha are not
>> satisfying this requirement as the barrier is after the register write.
>>
>> Move mb() in writeX() and iowriteX() functions to guarantee that HW
>> observes memory changes before performing register operations.
>>
>> Signed-off-by: Sinan Kaya <okaya@codeaurora.org>
>> Reported-by: Arnd Bergmann <arnd@arndb.de>
>> ---
>>  arch/alpha/kernel/io.c | 14 +++++++-------
>>  1 file changed, 7 insertions(+), 7 deletions(-)
> 
> Sorry for catching this late but this also needs to go to 4.17 after
> review.
> 
> I missed the writel() implementation on arch/alpha/kernel/io.c file
> on my first patch.
> 

Can you also queue this for 4.17?

There are already drivers checked into 4.17 that dropped the unnecessary
barriers. 

I really hate to see Alpha broken because of this.

Sinan

-- 
Sinan Kaya
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.