linux-kernel - Re: [PATCH v4 1/5] io: define several IO & PIO barrier types for the asm-generic version

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Date:   Fri, 6 Apr 2018 15:20:40 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Sinan Kaya <okaya@...eaurora.org>
Cc:     Timur Tabi <timur@...eaurora.org>, sulrich@...eaurora.org,
        linux-arm-msm@...r.kernel.org,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-s390 <linux-s390@...r.kernel.org>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Ley Foon Tan <lftan@...era.com>,
        "moderated list:NIOS2 ARCHITECTURE" 
        <nios2-dev@...ts.rocketboards.org>
Subject: Re: [PATCH v4 1/5] io: define several IO & PIO barrier types for the
 asm-generic version

On Fri, Apr 6, 2018 at 2:50 PM,  <okaya@...eaurora.org> wrote:
> On 2018-04-06 06:19, Arnd Bergmann wrote:
>>
>> On Thu, Apr 5, 2018 at 3:09 PM, Sinan Kaya <okaya@...eaurora.org> wrote:
>>>
>>
>> I would guess that at least s390 doesn't need the barriers
>> (maintainers on Cc now), but there may be others that want to
>> override the new barriers with weaker ones where an MMIO
>> access is guaranteed to serialize against DMA, or where
>> a specialized barrier for this case exists.
>>
>> Looking over the asm-generic implementation once more now,
>> I wonder if we should change the relaxed accessors to not have
>> any barriers (back to the version before your series) rather than
>> defaulting them to having the same barriers as the regular
>> readl/writel.
>
>
> I can do a follow up patch. You want to map them to raw api without any
> barriers as before. Right?

Right, but of course with the byteswap.

      Arnd