Re: [PATCH] docs/memory-barriers.txt: Fix broken DMA vs MMIO ordering example
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- To: Sinan Kaya <okaya@xxxxxxxxxxxxxx>
- Subject: Re: [PATCH] docs/memory-barriers.txt: Fix broken DMA vs MMIO ordering example
- From: Tony Luck <tony.luck@xxxxxxxxx>
- Date: Wed, 28 Mar 2018 10:57:11 -0700
- Cc: Paul McKenney <paulmck@xxxxxxxxxxxxxxxxxx>, Will Deacon <will.deacon@xxxxxxx>, "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>, linux-doc@xxxxxxxxxxxxxxx, Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>, Arnd Bergmann <arnd@xxxxxxxx>, Jason Gunthorpe <jgg@xxxxxxxx>, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Jonathan Corbet <corbet@xxxxxxx>, "linux-ia64@xxxxxxxxxxxxxxx" <linux-ia64@xxxxxxxxxxxxxxx>
- In-reply-to: <c93ed5db-8cfd-1258-3396-62ca2076c44d@codeaurora.org>
- References: <1522156287-15169-1-git-send-email-will.deacon@arm.com> <20180327150252.GN3675@linux.vnet.ibm.com> <c93ed5db-8cfd-1258-3396-62ca2076c44d@codeaurora.org>
On Wed, Mar 28, 2018 at 6:02 AM, Sinan Kaya <okaya@xxxxxxxxxxxxxx> wrote:
> +linux-ia64
> Does IA64 follow this requirement? If not, is implementation planned?
>
> "no wmb() before writel()"
>
> Linus asked us to get rid of wmb() in front of writel() for UC memory.
> Just checking that we are not breaking anything for IA64.
We should be OK on ia64, writel() uses a cast to:
*(volatile unsigned int __force *)
which the compiler takes as a request to use a "st4.rel" instruction
(meaning "store with release semantics"). So the value stored will
be visible to anything that follows.
-Tony
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