From mboxrd@z Thu Jan  1 00:00:00 1970
From: Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: RFC on writel and writel_relaxed
Date: Tue, 27 Mar 2018 20:14:07 -1000
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To: Sinan Kaya <okaya@codeaurora.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>, Alexander Duyck <alexander.duyck@gmail.com>, Will Deacon <will.deacon@arm.com>, Arnd Bergmann <arnd@arndb.de>, Jason Gunthorpe <jgg@ziepe.ca>, David Laight <David.Laight@aculab.com>, Oliver <oohall@gmail.com>, "open list:LINUX FOR POWERPC (32-BIT AND 64-BIT)" <linuxppc-dev@lists.ozlabs.org>, "linux-rdma@vger.kernel.org" <linux-rdma@vger.kernel.org>, Alexander Duyck <alexander.h.duyck@redhat.com>, "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>, "netdev@vger.kernel.org" <netdev@vger.kernel.org>
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On Tue, Mar 27, 2018 at 5:24 PM, Sinan Kaya <okaya@codeaurora.org> wrote:
>
> Basically changing it to
>
> dma_buffer->foo = 1;                    /* WB */
> wmb()
> writel_relaxed(KICK, DMA_KICK_REGISTER);        /* UC */
> mmiowb()

Why?

Why not  just remove the wmb(), and keep the barrier in the writel()?

The above code makes no sense, and just looks stupid to me. It also
generates pointlessly bad code on x86, so it's bad there too.

               Linus