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, 06 Apr 2018 08:50:50 -0400
From:   okaya@...eaurora.org
To:     Arnd Bergmann <arnd@...db.de>
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>, arndbergmann@...il.com
Subject: Re: [PATCH v4 1/5] io: define several IO & PIO barrier types for the
 asm-generic version

On 2018-04-06 06:19, Arnd Bergmann wrote:
> On Thu, Apr 5, 2018 at 3:09 PM, Sinan Kaya <okaya@...eaurora.org> 
> wrote:
>> Getting ready to harden readX()/writeX() and inX()/outX() semantics 
>> for the
>> generic implementation.
>> 
>> Defining two set of macros as __io_br() and __io_ar() to indicate 
>> actions
>> to be taken before and after MMIO read.
>> 
>> Defining two set of macros as __io_bw() and __io_aw() to indicate 
>> actions
>> to be taken before and after MMIO write.
>> 
>> Defining two set of macros as __io_pbw() and __io_paw() to indicate 
>> actions
>> to be taken before and after Port IO write.
>> 
>> Defining two set of macros as __io_pbr() and __io_par() to indicate 
>> actions
>> to be taken before and after Port IO read.
>> 
>> If rmb() is available for the architecture, prefer rmb() as the 
>> default
>> implementation of __io_ar()/__io_par().
>> 
>> If wmb() is available for the architecture, prefer wmb() as the 
>> default
>> implementation of __io_bw()/__io_pbw().
>> 
>> Signed-off-by: Sinan Kaya <okaya@...eaurora.org>
> 
> I've applied the series to my asm-generic tree now, I will give it a 
> few days
> in linux-next to see if any obvious regressions happen, and then send
> a pull request.
> 
> Checking the list of architectures that are affected by this, I see
> h8300, microblaze, nios2, openrisc, s390, sparc, um, unicore32,
> and xtensa, all of which use asm-generic/io.h without overriding
> the default readl/writel.
> 
> 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?


> 
>      Arnd