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Date: Wed, 13 Feb 2019 17:46:08 +0000
From: Will Deacon <will.deacon@arm.com>
Subject: Re: [PATCH 1/2] asm-generic/io: Pass result on inX() accessor to
 __io_par()
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To: Arnd Bergmann <arnd@arndb.de>
Cc: linux-arch <linux-arch@vger.kernel.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, andrew.murray@arm.com, Catalin Marinas <catalin.marinas@arm.com>, linux-riscv@lists.infradead.org, Palmer Dabbelt <palmer@sifive.com>, Albert Ou <aou@eecs.berkeley.edu>
Message-ID: <20190213174608.O0dl1JAPkNBjT2cfuHswadQ0qWTGfzOmSZJiNP4izxs@z>

On Tue, Feb 12, 2019 at 12:55:17PM +0100, Arnd Bergmann wrote:
> On Mon, Feb 11, 2019 at 6:45 PM Will Deacon <will.deacon@arm.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@arm.com>
> > Signed-off-by: Will Deacon <will.deacon@arm.com>
> > ---
> >  include/asm-generic/io.h | 8 ++++----
> 
> For changing the asm-generic file in the arm64 tree,
> 
> Acked-by: Arnd Bergmann <arnd@arndb.de>

Thanks, Arnd.

> 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.

There's already a comment in that header which says that the accesses are
ordered wrt timer reads, so I don't think anything needs to change there.
For consistency with the macro arguments, I could augment their __io_par to
take the read value as an unused argument, if that's what you mean?

Will