From: "Arnd Bergmann" <arnd@arndb.de>
To: "Parav Pandit" <parav@nvidia.com>,
stern@rowland.harvard.edu, parri.andrea@gmail.com,
"Will Deacon" <will@kernel.org>,
"Peter Zijlstra" <peterz@infradead.org>,
boqun.feng@gmail.com, "Nicholas Piggin" <npiggin@gmail.com>,
dhowells@redhat.com, j.alglave@ucl.ac.uk, luc.maranget@inria.fr,
"Paul E. McKenney" <paulmck@kernel.org>,
akiyks@gmail.com, dlustig@nvidia.com, joel@joelfernandes.org,
"Jonathan Corbet" <corbet@lwn.net>,
linux-kernel@vger.kernel.org,
Linux-Arch <linux-arch@vger.kernel.org>,
linux-doc@vger.kernel.org
Subject: Re: [PATCH] locking/memory-barriers.txt: Improve documentation for writel() usage
Date: Thu, 15 Sep 2022 14:37:57 +0200 [thread overview]
Message-ID: <96457b14-e196-4f29-be9a-7fa25ac805d9@www.fastmail.com> (raw)
In-Reply-To: <20220915050106.650813-1-parav@nvidia.com>
On Thu, Sep 15, 2022, at 7:01 AM, Parav Pandit wrote:
> The cited commit [1] describes that when using writel(), explcit wmb()
> is not needed. However, it should have said that dma_wmb() is not
> needed.
Are you sure? As I understand it, the dma_wmb() only serializes
a set of memory accesses, but does not serialized against an MMIO
access, which depending on the CPU architecture may require a
different type of barrier.
E.g. on arm, writel() uses __iowmb(), which like wmb() is defined
as "dsb(x); arm_heavy_mb();", while dma_wmb() is a "dmb(oshst)".
Arnd
next prev parent reply other threads:[~2022-09-15 12:38 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-15 5:01 Parav Pandit
2022-09-15 12:16 ` Bagas Sanjaya
2022-09-15 12:35 ` Parav Pandit
2022-09-15 12:37 ` Arnd Bergmann [this message]
2022-09-15 14:18 ` Parav Pandit
2022-09-15 15:16 ` Arnd Bergmann
2022-09-15 16:35 ` Parav Pandit
2022-09-15 18:38 ` Arnd Bergmann
2022-09-23 15:55 ` Parav Pandit
2022-09-23 18:40 ` Arnd Bergmann
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