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    SubjectRe: [PATCH V2 0/4] misc: xgene: Add support for APM X-Gene SoC Queue Manager/Traffic Manager
    On Sat, Jan 04, 2014 at 03:59:46PM -0800, Ravi Patel wrote:
    > On Sat, Dec 21, 2013 at 11:03 PM, Arnd Bergmann <arnd@arndb.de> wrote:
    > > On Saturday 21 December 2013 17:00:51 Loc Ho wrote:
    > >> On Sat, Dec 21, 2013 at 12:11 PM, Arnd Bergmann <arnd@arndb.de> wrote:
    > >> > On Saturday 21 December 2013, Ravi Patel wrote:
    > >> >> This patch adds support for APM X-Gene SoC Queue Manager/Traffic Manager.
    > >> >> QMTM is required by APM X-Gene SoC Ethernet, PktDMA (XOR Engine) and
    > >> >> Security Engine subsystems. All subsystems communicate with QMTM using
    > >> >> messages which include information about the work to be performed and
    > >> >> the location of associated data buffers.
    > >> >
    > >> > Please describe here what the purpose of the qmtm is, as this is not
    > >> > entirely clear from the code.
    > >> >
    > >> > In particular, please describe how this differs from a dmaengine driver
    > >> > and why it is not possible to extend the dma slave API to describe qmtm
    > >> > as a dma engine.
    > >> >
    > >> [Loc Ho]
    > >> If the QM driver implements the DMA API, what about the actual DMA
    > >> engine driver which interfaces with this QM driver. We would have DMA
    > >> client interfaces with the X-Gene DMA driver (not available yet) via
    > >> DMA API which in turn interfaces with this QM driver via DMA API.
    > >> Won't this be kind of awkward? Also, the QM only manage messages (or
    > >> descriptors) which are 32-bytes or 64-bytes. It doesn't actually do
    > >> any data transfer of various sizes.
    > >
    > > Please describe here what the purpose of the qmtm is, as this is not
    > > entirely clear from the code or from your reply.
    > >
    > > Greg was guessing that it's a bus controller, my best guess is a DMA
    > > engine. If it's something completely different, you have to let
    > > us know what it is so we can do a proper review rather than guessing.
    > >
    > > Please provide a link to the data sheet if you are unable to explain.
    >
    > Here is URL to a text document explaining role of QMTM device with CPU, Ethernet
    > subsystem.
    >
    > https://drive.google.com/file/d/0B28TgQZ3JLoRRGNnbjJoUGNHWW8/edit?usp=sharing

    There is nothing at this link :(

    > PktDMA and Security subsystem interfaces with QMTM in the same way as Ethernet.

    How does a "security" subsystem have anything to do with ethernet?

    confused,

    greg k-h


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