From: Arnd Bergmann <arnd.bergmann@linaro.org>
To: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Hein Tibosch <hein_tibosch@yahoo.es>,
"Hans-Christian Egtvedt" <hans-christian.egtvedt@atmel.com>,
Nicolas Ferre <nicolas.ferre@atmel.com>,
Havard Skinnemoen <havard@skinnemoen.net>,
"ludovic.desroches" <ludovic.desroches@atmel.com>,
linux-kernel@vger.kernel.org,
"spear-devel" <spear-devel@list.st.com>
Subject: Re: [PATCH] Fixes for dw_dmac and atmel-mci for AP700x
Date: Tue, 21 Aug 2012 08:34:53 +0000 [thread overview]
Message-ID: <201208210834.53544.arnd.bergmann@linaro.org> (raw)
In-Reply-To: <CAKohpomMPeewDBVxVR=g-op7E53rqt-AZgOdyoib6W+5QsLOOA@mail.gmail.com>
On Tuesday 21 August 2012, Viresh Kumar wrote:
> On 21 August 2012 13:02, Hein Tibosch <hein_tibosch@yahoo.es> wrote:
>
> > On 8/21/2012 2:35 PM, Viresh Kumar wrote:
> >
> > It got swapped as 0xAABB.CCDD => 0xCCDD.AABB
> >
>
> @Arnd: How do we explain this? shouldn't it be DD CC BB AA??
Yes, this is very strange. Maybe the compiler already splits the
access into two 16-byte loads and that confuses the device?
> > Memory barriers: within the AVR32 code, one often sees explicit ways to
> > introduce memory barriers, e.g.:
> >
> > hsmc_readl(hsmc, MODE0); /* I/O barrier */
> >
>
> For ARM it has become a bit complex about using barriers. That's why they
> are added in readl/writel to remove any confusion.
To be more exact: the reason why readl/writel have the barriers is that
device drivers written for x86 expect the barrier semantics to be implied.
ARM also has readl_relaxed/writel_relaxed, which don't have a barrier
against DMA but still enforce ordering between the readl calls (implied
by the CPU architecture).
Arnd
next prev parent reply other threads:[~2012-08-21 8:36 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <502BC31E.4070200@yahoo.es>
[not found] ` <502BDD0E.4030106@yahoo.es>
[not found] ` <502CA8FC.7090705@atmel.com>
[not found] ` <502CB89B.4070302@yahoo.es>
[not found] ` <502CC326.8020605@atmel.com>
[not found] ` <502CC6A0.3050603@atmel.com>
[not found] ` <502F52E7.9050804@yahoo.es>
[not found] ` <CACiLriS-GZg24TJqJGQ=P04n-Zk3FdHtGgh5VeqGcCMHG6TnMw@mail.gmail.com>
[not found] ` <50310F10.2080701@yahoo.es>
2012-08-21 4:42 ` [PATCH] Fixes for dw_dmac and atmel-mci for AP700x viresh kumar
2012-08-21 6:12 ` Hein Tibosch
[not found] ` <CAKohponN16krs-WWw6Abh1fLPO3+iYndTaxsPDfeXCoS9OHufQ@mail.gmail.com>
2012-08-21 7:32 ` Hein Tibosch
[not found] ` <CAKohpomMPeewDBVxVR=g-op7E53rqt-AZgOdyoib6W+5QsLOOA@mail.gmail.com>
2012-08-21 8:34 ` Arnd Bergmann [this message]
[not found] ` <CAKohpokhM5WkUK6ww8Neu+fx554+-4uBCsNzBxB9q5rcqSf6cw@mail.gmail.com>
2012-08-21 8:47 ` Arnd Bergmann
[not found] ` <CAKohpokoeSLBtLdh8hr4GKv8VOxzK8Vq5SoqLE3yC-TDyjYA9w@mail.gmail.com>
2012-08-21 9:05 ` Arnd Bergmann
2012-08-21 14:24 ` Hein Tibosch
2012-08-21 7:44 ` Arnd Bergmann
[not found] ` <CAKohpo=DyQajiE-DmpMiv=gVOVOep1OEECVuw83D2u4VJisEsw@mail.gmail.com>
2012-08-21 8:31 ` Arnd Bergmann
2012-08-21 14:15 ` Havard Skinnemoen
2012-08-23 3:47 ` Hein Tibosch
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