linux-kernel - Re: [STLinux Kernel] [PATCH v11 17/19] serial: asc: Adopt readl_/writel

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Message-ID: <20140902134257.GA10125@griffinp-ThinkPad-X1-Carbon-2nd>
Date:	Tue, 2 Sep 2014 14:42:58 +0100
From:	Peter Griffin <peter.griffin@...aro.org>
To:	Daniel Thompson <daniel.thompson@...aro.org>
Cc:	Russell King <linux@....linux.org.uk>, kernel@...inux.com,
	Catalin Marinas <catalin.marinas@....com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Fabio Estevam <festevam@...il.com>,
	Nicolas Pitre <nico@...aro.org>, Jiri Slaby <jslaby@...e.cz>,
	Anton Vorontsov <anton.vorontsov@...aro.org>,
	Ben Dooks <ben.dooks@...ethink.co.uk>,
	Rob Herring <robherring2@...il.com>,
	linux-serial@...r.kernel.org, kgdb-bugreport@...ts.sourceforge.net,
	kernel-team@...roid.com, Dave Martin <Dave.Martin@....com>,
	linaro-kernel@...ts.linaro.org, patches@...aro.org,
	John Stultz <john.stultz@...aro.org>,
	linux-arm-kernel@...ts.infradead.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, Colin Cross <ccross@...roid.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Srinivas Kandagatla <srinivas.kandagatla@...il.com>
Subject: Re: [STLinux Kernel] [PATCH v11 17/19] serial: asc: Adopt
 readl_/writel_relaxed()

On Tue, 02 Sep 2014, Daniel Thompson wrote:

> The architectures where this peripheral exists (ARM and SH) have expensive
> implementations of writel(), reliant on spin locks and explicit L2 cache
> management. These architectures provide a cheaper writel_relaxed() which
> is much better suited to peripherals that do not perform DMA. The
> situation with readl()/readl_relaxed()is similar although less acute.
> 
> This driver does not use DMA and will be more power efficient and more
> robust (due to absense of spin locks during console I/O) if it uses the
> relaxed variants.
> 
> This change means the driver is no longer portable and therefore no
> longer suitable for compile testing.
> 
> Signed-off-by: Daniel Thompson <daniel.thompson@...aro.org>
> Cc: Srinivas Kandagatla <srinivas.kandagatla@...il.com>
> Cc: Maxime Coquelin <maxime.coquelin@...com>
> Cc: Patrice Chotard <patrice.chotard@...com>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: Jiri Slaby <jslaby@...e.cz>
> Cc: kernel@...inux.com
> Cc: linux-serial@...r.kernel.org

Acked-by: Peter Griffin <peter.griffin@...aro.org>

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