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

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Message-ID: <CAEdQ38GY9ZtNqOt1ZSetwZjyKAokY6-qEVy1t+t=_FEqx+-+zQ@mail.gmail.com>
Date:   Tue, 8 May 2018 19:57:53 -0700
From:   Matt Turner <mattst88@...il.com>
To:     Sinan Kaya <okaya@...eaurora.org>
Cc:     linux-alpha <linux-alpha@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Timur Tabi <timur@...eaurora.org>, sulrich@...eaurora.org,
        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>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] alpha: io: reorder barriers to guarantee writeX() and
 iowriteX() ordering #2

On Fri, Apr 20, 2018 at 9:20 AM, Sinan Kaya <okaya@...eaurora.org> wrote:
> 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.

Yes, I will pick it up for 4.17.

Thanks for the patch.