linux-kernel - Re: [PATCH 1/2] asm-generic/io: Pass result on inX() accessor to __io

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Date:   Tue, 12 Feb 2019 12:55:17 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Will Deacon <will.deacon@....com>
Cc:     linux-arch <linux-arch@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        andrew.murray@....com, Catalin Marinas <catalin.marinas@....com>,
        linux-riscv@...ts.infradead.org,
        Palmer Dabbelt <palmer@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>
Subject: Re: [PATCH 1/2] asm-generic/io: Pass result on inX() accessor to __io_par()

On Mon, Feb 11, 2019 at 6:45 PM Will Deacon <will.deacon@....com> wrote:
>
> The inX() I/O accessors must enforce ordering against subsequent calls
> to the delay() routines, so that a read-back from a device can be used
> to postpone a subsequent write to the same device.
>
> On some architectures, including arm64, this ordering can only be
> achieved by creating a dependency on the value returned by the inX()
> operation, so we need to pass the value we read to the __io_par()
> macro in this case.
>
> Reported-by: Andrew Murray <andrew.murray@....com>
> Signed-off-by: Will Deacon <will.deacon@....com>
> ---
>  include/asm-generic/io.h | 8 ++++----

For changing the asm-generic file in the arm64 tree,

Acked-by: Arnd Bergmann <arnd@...db.de>

For all I can see, this should not conflict with the usage of the
same macros on RISC-V, though it does make add a significant
difference, so I'd like to see an Ack from the RISC-V folks as
well (added to Cc), or possibly a change to arch/riscv/include/asm/io.h
to do a corresponding change.

       Arnd