From: Marek Vasut <marex@denx.de>
To: "Russell King - ARM Linux" <linux@arm.linux.org.uk>
Subject: Re: [PATCH linux-next v4 5/5] mtd: atmel-quadspi: add driver for Atmel QSPI controller
Date: Mon, 24 Aug 2015 15:15:44 +0200
User-Agent: KMail/1.13.7 (Linux/3.14-2-amd64; KDE/4.13.1; x86_64; ; )
Cc: Cyrille Pitchen <cyrille.pitchen@atmel.com>, mark.rutland@arm.com,
        devicetree@vger.kernel.org, pawel.moll@arm.com,
        ijc+devicetree@hellion.org.uk, ben@decadent.org.uk, zajec5@gmail.com,
        nicolas.ferre@atmel.com, linux-kernel@vger.kernel.org,
        robh+dt@kernel.org, linux-spi@vger.kernel.org, juhosg@openwrt.org,
        broonie@kernel.org, linux-mtd@lists.infradead.org,
        galak@codeaurora.org, shijie.huang@intel.com,
        computersforpeace@gmail.com, dwmw2@infradead.org,
        linux-arm-kernel@lists.infradead.org, beanhuo@micron.com
References: <cover.1440410236.git.cyrille.pitchen@atmel.com> <201508241303.52066.marex@denx.de> <20150824124924.GZ7557@n2100.arm.linux.org.uk>
In-Reply-To: <20150824124924.GZ7557@n2100.arm.linux.org.uk>
MIME-Version: 1.0
Content-Type: Text/Plain;
  charset="us-ascii"
Content-Transfer-Encoding: 7bit
Message-Id: <201508241515.45036.marex@denx.de>
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1427
Lines: 39

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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/