Re: [PATCH linux-next v4 5/5] mtd: atmel-quadspi: add driver for Atmel QSPI controller

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From	Marek Vasut <marex@denx.de>
Newsgroups	linux.kernel
Subject	Re: [PATCH linux-next v4 5/5] mtd: atmel-quadspi: add driver for Atmel QSPI controller
Date	Mon, 24 Aug 2015 15:20:02 +0200
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X-Original-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
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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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Thread

[PATCH linux-next v4 5/5] mtd: atmel-quadspi: add driver for Atmel QSPI controller Cyrille Pitchen <cyrille.pitchen@atmel.com> - 2015-08-24 12:20 +0200
  Re: [PATCH linux-next v4 5/5] mtd: atmel-quadspi: add driver for Atmel QSPI controller Marek Vasut <marex@denx.de> - 2015-08-24 13:10 +0200
    Re: [PATCH linux-next v4 5/5] mtd: atmel-quadspi: add driver for  Atmel QSPI controller Russell King - ARM Linux <linux@arm.linux.org.uk> - 2015-08-24 15:00 +0200
      Re: [PATCH linux-next v4 5/5] mtd: atmel-quadspi: add driver for Atmel QSPI controller Marek Vasut <marex@denx.de> - 2015-08-24 15:20 +0200
    Re: [PATCH linux-next v4 5/5] mtd: atmel-quadspi: add driver for  Atmel QSPI controller Cyrille Pitchen <cyrille.pitchen@atmel.com> - 2015-08-24 19:10 +0200
      Re: [PATCH linux-next v4 5/5] mtd: atmel-quadspi: add driver for Atmel QSPI controller Marek Vasut <marex@denx.de> - 2015-08-24 19:50 +0200
        Re: [PATCH linux-next v4 5/5] mtd: atmel-quadspi: add driver for  Atmel QSPI controller Jonas Gorski <jogo@openwrt.org> - 2015-08-25 11:50 +0200
          Re: [PATCH linux-next v4 5/5] mtd: atmel-quadspi: add driver for  Atmel QSPI controller Cyrille Pitchen <cyrille.pitchen@atmel.com> - 2015-08-25 12:30 +0200
    Re: [PATCH linux-next v4 5/5] mtd: atmel-quadspi: add driver for  Atmel QSPI controller Cyrille Pitchen <cyrille.pitchen@atmel.com> - 2015-08-25 12:20 +0200
      Re: [PATCH linux-next v4 5/5] mtd: atmel-quadspi: add driver for Atmel QSPI controller Marek Vasut <marex@denx.de> - 2015-08-25 12:30 +0200
        Re: [PATCH linux-next v4 5/5] mtd: atmel-quadspi: add driver for  Atmel QSPI controller Brian Norris <computersforpeace@gmail.com> - 2015-08-25 18:00 +0200
  RE: [PATCH linux-next v4 5/5] mtd: atmel-quadspi: add driver for  Atmel QSPI controller Bean Huo 霍斌斌 (beanhuo)   <beanhuo@micron.com> - 2015-08-25 03:50 +0200
    Re: [PATCH linux-next v4 5/5] mtd: atmel-quadspi: add driver for  Atmel QSPI controller Cyrille Pitchen <cyrille.pitchen@atmel.com> - 2015-08-25 13:30 +0200

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