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    SubjectRe: [PATCH 3/3 v2] dmaengine: Add Freescale i.MX SDMA support
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    Dne So 28. srpna 2010 18:18:58 Sascha Hauer napsal(a):
    > On Sat, Aug 28, 2010 at 05:27:10PM +0200, Marek Vasut wrote:
    > > Dne So 28. srpna 2010 17:18:17 Linus Walleij napsal(a):
    > > > 2010/8/23 Uwe Kleine-König <u.kleine-koenig@pengutronix.de>:
    > > > >> + evt = readl(SDMA_H_EVTOVR);
    > > > >> + mcu = readl(SDMA_H_HOSTOVR);
    > > > >> + dsp = readl(SDMA_H_DSPOVR);
    > > > >
    > > > > __raw_readl?
    > > >
    > > > Sorry I never understood this __raw_[read|write][b|w|l] vs.
    > > > plain read[b|w|l] proliferation in some drivers and code.
    > > >
    > > > What's the reason for?
    > >
    > > Hey,
    > >
    > > this trick is, if you create the VA<->PA mapping at the kernel start (eg.
    > > see how pxa_map_io() is replacedon some devices for instance), you then
    > > use the VA address you specified and use __raw_{read,write}[b,w,l](). So
    > > use __raw_{read,write}[b,w,l]() on drivers specific for certain device
    > > and use {read,write}[b,w,l]() on ioremap()ed memory areas, aka. in
    > > common drivers.
    >
    > Nope, this has nothing to do with static mappings vs. ioremap. The
    > difference is that read[b,w,l] do little endian accesses suitable for
    > PCI whereas the __raw_* functions do accesses in CPU endianess.
    > Peripherals integrated into a SoC like the SDMA engine here are
    > normally accessible in native endianess and thus need the __raw_*
    > functions. An external network controller (for example a LAN9117) will
    > probably need the non raw functions. Note that 99% of the arm users use
    > little endian only and thus cpu_to_le* is a noop, so both types will work
    > for most people.

    Sorry, you got me here. Why do we have io{read,write} then btw. ? That's for
    x86's io space, right ?

    Thanks, cheers and sorry for the confusion
    >
    > Sascha
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