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Message-Id: <201508241515.45036.marex@denx.de>
Date: Mon, 24 Aug 2015 15:15:44 +0200
From: Marek Vasut <marex@...x.de>
To: "Russell King - ARM Linux" <linux@....linux.org.uk>
Cc: Cyrille Pitchen <cyrille.pitchen@...el.com>, mark.rutland@....com,
devicetree@...r.kernel.org, pawel.moll@....com,
ijc+devicetree@...lion.org.uk, ben@...adent.org.uk,
zajec5@...il.com, nicolas.ferre@...el.com,
linux-kernel@...r.kernel.org, robh+dt@...nel.org,
linux-spi@...r.kernel.org, juhosg@...nwrt.org, broonie@...nel.org,
linux-mtd@...ts.infradead.org, galak@...eaurora.org,
shijie.huang@...el.com, computersforpeace@...il.com,
dwmw2@...radead.org, linux-arm-kernel@...ts.infradead.org,
beanhuo@...ron.com
Subject: Re: [PATCH linux-next v4 5/5] mtd: atmel-quadspi: add driver for Atmel QSPI controller
On Monday, August 24, 2015 at 02:49:24 PM, Russell King - ARM Linux wrote:
Hi Russell,
> On Mon, Aug 24, 2015 at 01:03:51PM +0200, Marek Vasut wrote:
> > These are functions, not macros :)
> >
> > btw is there any reason for these ? I'd say, just put the read*() and
> > write*() functions directly into the code and be done with it, it is
> > much less confusing.
> >
> > Also, why do you use the _relaxed() versions of the functions ?
>
> Now that the _relaxed() accessors are available throughout the kernel,
> everyone should be using the _relaxed() versions unless they need the
> properties of the non-relaxed versions.
You mean the memory barrier, right ?
> Remember that the non-relaxed
> versions are rather expensive on ARM due to the need to go all the way
> out to the L2 cache - it at least doubles the number of accesses for
> every read*/write*().
I think in case of this driver, we don't need the non-relaxed version
anywhere, right ? Thanks for the educational writeup :)
btw. is [1] still the current study material on the I/O accessor best
practices please ?
[1] http://permalink.gmane.org/gmane.linux.ports.arm.kernel/117644
Best regards,
Marek Vasut
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