linux-kernel - Re: [PATCH] net: emac: emac gigabit ethernet controller driver

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Message-ID: <1579270.z2ZaCA4LQo@wuerfel>
Date:	Tue, 15 Dec 2015 16:41:18 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Timur Tabi <timur@...eaurora.org>
Cc:	Christopher Covington <cov@...eaurora.org>,
	Florian Fainelli <f.fainelli@...il.com>,
	Gilad Avidov <gavidov@...eaurora.org>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
	linux-arm-msm@...r.kernel.org, sdharia@...eaurora.org,
	shankerd@...eaurora.org, gregkh@...uxfoundation.org,
	vikrams@...eaurora.org
Subject: Re: [PATCH] net: emac: emac gigabit ethernet controller driver

On Tuesday 15 December 2015 09:17:00 Timur Tabi wrote:
> Arnd Bergmann wrote:
> > We generally want to use readl/writel rather than the relaxed versions,
> > unless it is in performance-critical code.
> 
> What about if we have 20+ writes in a row, for example, when 
> initializing a part?  I've seen code like this:
> 
>         writel_relaxed(...);
>         writel_relaxed(...);
>         writel_relaxed(...);
>         ...
>         writel(...); // HW now inited, so enable

If that's in the probe() called from it function, just use writel() everywhere,
a few extra microseconds won't kill the boot time. In general, if a user would
notice the difference, use the relaxed version and add a comment to explain
how you proved it's correct, otherwise stay with the default accessors.

	Arnd
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