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    SubjectRe: [PATCHv2] DMAEngine: Let dmac drivers to set chan_id
    On Thu, Jul 28, 2011 at 11:24:12PM +0530, Jaswinder Singh wrote:
    > On 28 July 2011 02:07, Russell King <rmk@arm.linux.org.uk> wrote:
    > >
    > >> On a serious note, my proposal, and the reply, shows the possibility
    > >> of having :-
    > >> a) Client drivers that are truly platform agnostic -- no platform_data
    > >> poking for
    > >>       channel selection
    > >
    > > I really doubt that's even possible.  Take this setup:
    >
    > I don't want to suggest anything wrong just because I didn't understand
    > your h/w.
    > I hope you will be kind enough to help me better understand your setup,
    > so that I have a fair chance to present my proposal.
    >
    > A simple 'yes' or a 'no'(with clarification) is all I ask.
    >
    > >
    > > MMCI ---> DMAC
    > >
    > > where the DMAC has 32 request signals, and 8 channels.
    > The DMAC is similar to PL330.

    That coincidence is merely that.

    > Only max 8 request-signals can be active at any time.
    > Is my understanding right ?

    Correct.

    > > The MMCI is connected to two of them.
    > I don't know anything about MMCI.
    > So I assume it is just another third party MMC controller.
    > It simply needs 2 dma channels(for RX, TX each) - be it from a DMAC
    > that has a programmable RequestSignal->Peripheral map or a fixed map.
    > Is my understanding right ?

    Correct.

    > > The DMAC can supply any of its physical channels for MMCI.
    > The RequestSignal->Peripheral map is decided during board design
    > and can not be changed later.
    > Is my understanding right ?

    No. See the board#3 case..

    > > Board 1 has the MMCI connected to request signals #1 and #3.
    > > Board 2 has the MMCI connected to request signals #8 and #22.
    > Say,
    > Board1
    > MMCI_RX -> #1
    > MMCI_TX -> #3
    >
    > Board2
    > MMCI_RX -> #8
    > MMCI_TX -> #22
    >
    > > Board 3 has the MMCI connected through an external FPGA mux, which can route the
    > > MMCI requests to DMA request signals #1, #2 or #3.
    > Say
    > Board3
    > MMCI_RX -> #{1,2,3}
    > MMCI_TX -> #{1,2,3}
    > And you can't change the route(mapping) after the dmac driver has
    > been loaded.

    No. You have to change it dynamically at run time according to the
    DMA activity, because DMA request signals #1, #2 and #3 are shared
    between 6 devices. To make matters worse, it's not six on any of
    RQ#1 RQ#2 RQ#3, but some on a couple, some on another couple, and
    some on all three.

    BTW, we do support this with Linus W's code (which he's posted to
    this thread.)

    --
    Russell King
    Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/
    maintainer of:
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