linux-kernel - Re: [PATCHv5 1/4] arm64: io: Use asm-generic high level MMIO accessors

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Date:   Mon, 6 Dec 2021 12:30:45 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Sai Prakash Ranjan <quic_saipraka@...cinc.com>
Cc:     Arnd Bergmann <arnd@...db.de>, Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Marc Zyngier <maz@...nel.org>,
        gregkh <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        quic_psodagud@...cinc.com
Subject: Re: [PATCHv5 1/4] arm64: io: Use asm-generic high level MMIO accessors

On Mon, Dec 6, 2021 at 12:12 PM Sai Prakash Ranjan
<quic_saipraka@...cinc.com> wrote:
> On 12/6/2021 2:20 PM, Arnd Bergmann wrote:
> > I think it would be even better to flip these around and make the low-level
> > definitions __io_ar() and __io_bw(), and then defining the arm64 specific
> > macros based on those:
> >
> > /* arm64-specific, don't use in portable drivers */
> > #define __iormb(v)     __io_ar(v)
> > #define __iowmb()      __io_bw()
> > #define __iomb()        dma_mb()
> >
> >
>
> So __iormb on arm64 has some dummy control dependency stuff as well based on
> ("arm64: io: Ensure calls to delay routines are ordered against prior
> readX()") and then we would need to change __iormb definition to __io_ar which
> doesn't seem like __iormb definition to be exact right?

I'm not sure what you are asking here. As far as I can tell, __io_ar()
and __iormb() have the same calling conventions and the same barrier
requirements, so they should be interchangeable, we just need to decide
which one is the primary definition.

       Arnd