linux-kernel - Re: [PATCH] alpha: io: reorder barriers to guarantee writeX() and iowriteX() ordering #2

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Date:   Fri, 20 Apr 2018 12:20:11 -0400
From:   Sinan Kaya <okaya@...eaurora.org>
To:     linux-alpha@...r.kernel.org, arnd@...db.de, timur@...eaurora.org,
        sulrich@...eaurora.org, Matt Turner <mattst88@...il.com>
Cc:     linux-arm-msm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Richard Henderson <rth@...ddle.net>,
        Ivan Kokshaysky <ink@...assic.park.msu.ru>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] alpha: io: reorder barriers to guarantee writeX() and
 iowriteX() ordering #2

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@...eaurora.org>
>> Reported-by: Arnd Bergmann <arnd@...db.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.