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    SubjectRe: [PATCH 3/3 v2] dmaengine: Add Freescale i.MX SDMA support
    On Sat, Aug 28, 2010 at 06:30:05PM +0200, Marek Vasut wrote:
    > Dne So 28. srpna 2010 18:18:58 Sascha Hauer napsal(a):
    > > 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 ?

    io{read,write} are for use with ioremap/ioport_map, and allow drivers to
    be written which can access registers via MMIO or the PC IO space.

    If your driver doesn't support the PC IO space (iow, doesn't use
    ioport_map) there's no point using the io{read,write} APIs.

    Also note that there's one very big difference between read[bwl] and
    __raw_read[bwl]. The former have a barrier to ensure correct ordering
    for drivers doing DMA, the latter do not. So if you use the latter and
    you care about data being visible to a DMA agent, you have to ensure
    you have proper barriers in place.

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      Last update: 2010-09-02 13:23    [W:0.024 / U:0.024 seconds]
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