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Message-ID: <20210723164158.GJ5221@sirena.org.uk>
Date: Fri, 23 Jul 2021 17:41:58 +0100
From: Mark Brown <broonie@...nel.org>
To: Arnd Bergmann <arnd@...db.de>
Cc: Clément Léger <clement.leger@...tlin.com>,
Lee Jones <lee.jones@...aro.org>,
Rob Herring <robh+dt@...nel.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
"Rafael J. Wysocki" <rafael@...nel.org>,
DTML <devicetree@...r.kernel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Peng Fan <peng.fan@....com>,
Sudeep Holla <sudeep.holla@....com>,
Alexandre Belloni <alexandre.belloni@...tlin.com>
Subject: Re: [PATCH 2/3] syscon: add support for "syscon-smc" compatible
On Fri, Jul 23, 2021 at 06:07:44PM +0200, Arnd Bergmann wrote:
> There is also a problem with locking: In the case that both firmware and
> kernel have to access registers within a syscon area, you may need to
> have a semaphore to protect an atomic sequence of accesses, but since
> the interface only provides a single register load/store, there is no way for
> a kernel driver to serialize against a firmware-internal driver.
The standard solution to this for the read/modify/write case would be to
expose an explicit update_bits() operation (some hardware does this for
concurrency and/or bus bandwidth/latency reasons), though that doesn't
help with larger or multi-register sequences (and to be clear as I've
been saying I don't think we should do this at all).
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