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    SubjectRe: [PATCH 1/3] DMAENGINE: generic slave channel control
    From
    Hi Dan,

    any thoughts on this? Personally I really like this abstraction from
    my experience with embedded DMA controllers, but I don't have your
    wide experience of DMA hardware.

    Yours,
    Linus Walleij

    2010/6/29 Linus Walleij <linus.walleij@stericsson.com>:
    > This adds an interface to the DMAengine to make it possible to
    > reconfigure a slave channel at runtime. We add a few foreseen
    > config parameters to the passed struct, with a void * pointer
    > for custom per-device or per-platform runtime slave data.
    >
    > Signed-off-by: Linus Walleij <linus.walleij@stericsson.com>
    > ---
    >  include/linux/dmaengine.h |   48 +++++++++++++++++++++++++++++++++++++++++++++
    >  1 files changed, 48 insertions(+), 0 deletions(-)
    >
    > diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
    > index 5204f01..e2601bd 100644
    > --- a/include/linux/dmaengine.h
    > +++ b/include/linux/dmaengine.h
    > @@ -114,11 +114,17 @@ enum dma_ctrl_flags {
    >  * @DMA_TERMINATE_ALL: terminate all ongoing transfers
    >  * @DMA_PAUSE: pause ongoing transfers
    >  * @DMA_RESUME: resume paused transfer
    > + * @DMA_SLAVE_CONFIG: this command is only implemented by DMA controllers
    > + * that need to runtime reconfigure the slave channels (as opposed to passing
    > + * configuration data in statically from the platform). An additional
    > + * argument of struct dma_slave_config must be passed in with this
    > + * command.
    >  */
    >  enum dma_ctrl_cmd {
    >        DMA_TERMINATE_ALL,
    >        DMA_PAUSE,
    >        DMA_RESUME,
    > +       DMA_SLAVE_CONFIG,
    >  };
    >
    >  /**
    > @@ -199,6 +205,48 @@ struct dma_chan_dev {
    >        atomic_t *idr_ref;
    >  };
    >
    > +/**
    > + * struct dma_slave_config - dma slave channel runtime config
    > + * @addr: this is the physical address where DMA slave data should be
    > + * read (RX) or written (TX)
    > + * @addr_width: this is the width of the source (RX) or target
    > + * (TX) register where DMA data shall be read/written, in bytes.
    > + * legal values: 1, 2, 4, 8.
    > + * @direction: whether the data shall go in or out on this slave
    > + * channel, right now.
    > + * @maxburst: the maximum number of words (note: words, as in units
    > + * of the addr_width member, not bytes) that can be sent in one burst
    > + * to the device. Typically something like half the FIFO depth on
    > + * I/O peripherals so you don't overflow it.
    > + * @private_config: if you need to pass in specialized configuration
    > + * at runtime, apart from the generic things supported in this
    > + * struct, you provide it in this pointer and dereference it inside
    > + * your dmaengine driver to get the proper configuration bits out.
    > + *
    > + * This struct is passed in as configuration data to a DMA engine
    > + * in order to set up a certain channel for DMA transport at runtime.
    > + * The DMA device/engine has to provide support for an additional
    > + * command in the channel config interface, DMA_SLAVE_CONFIG
    > + * and this struct will then be passed in as an argument to the
    > + * DMA engine device_control() function.
    > + *
    > + * The rationale for adding configuration information to this struct
    > + * is as follows: if it is likely that most DMA slave controllers in
    > + * the world will support the configuration option, then make it
    > + * generic. If not, if it is fixed so that it be sent in static from
    > + * the platform data, then prefer to do that. Else, if it is neither
    > + * fixed, not generic enough (such as bus mastership on some CPU
    > + * family and whatnot) then pass it in the private_config member
    > + * and dereference it to some per-device struct in your driver.
    > + */
    > +struct dma_slave_config {
    > +       dma_addr_t addr;
    > +       u8 addr_width:4;
    > +       enum dma_data_direction direction;
    > +       int maxburst;
    > +       void *private_config;
    > +};
    > +
    >  static inline const char *dma_chan_name(struct dma_chan *chan)
    >  {
    >        return dev_name(&chan->dev->device);
    > --
    > 1.7.0.1
    >
    > --
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