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    Subject[PATCH] DMAEngine: Define generic transfer request api
    Date
    Define a new api that could be used for doing fancy data transfers
    like interleaved to contiguous copy and vice-versa.
    Traditional SG_list based transfers tend to be very inefficient in
    such cases as where the interleave and chunk are only a few bytes,
    which call for a very condensed api to convey pattern of the transfer.

    This api supports all 4 variants of scatter-gather and contiguous transfer.
    Besides, it could also represent common operations like
    device_prep_dma_{cyclic, memset, memcpy}
    and maybe some more that I am not sure of.

    Of course, neither can this api help transfers that don't lend to DMA by
    nature, i.e, scattered tiny read/writes with no periodic pattern.

    Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>
    ---
    include/linux/dmaengine.h | 73 +++++++++++++++++++++++++++++++++++++++++++++
    1 files changed, 73 insertions(+), 0 deletions(-)

    diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
    index 8fbf40e..74f3ae0 100644
    --- a/include/linux/dmaengine.h
    +++ b/include/linux/dmaengine.h
    @@ -76,6 +76,76 @@ enum dma_transaction_type {
    /* last transaction type for creation of the capabilities mask */
    #define DMA_TX_TYPE_END (DMA_CYCLIC + 1)

    +/**
    + * Generic Transfer Request
    + * ------------------------
    + * A chunk is collection of contiguous bytes to be transfered.
    + * The gap(in bytes) between two chunks is called inter-chunk-gap(ICG).
    + * ICGs may or maynot change between chunks.
    + * A FRAME is the smallest series of contiguous {chunk,icg} pairs,
    + * that when repeated an integral number of times, specifies the transfer.
    + * A transfer template is specification of a Frame, the number of times
    + * it is to be repeated and other per-transfer attributes.
    + *
    + * Practically, a client driver would have ready a template for each
    + * type of transfer it is going to need during its lifetime and
    + * set only 'src_start' and 'dst_start' before submitting the requests.
    + *
    + *
    + * | Frame-1 | Frame-2 | ~ | Frame-'numf' |
    + * |====....==.===...=...|====....==.===...=...| ~ |====....==.===...=...|
    + *
    + * == Chunk size
    + * ... ICG
    + */
    +
    +/**
    + * struct data_chunk - Element of scatter-gather list that makes a frame.
    + * @size: Number of bytes to read from source.
    + * size_dst := fn(op, size_src), so doesn't mean much for destination.
    + * @icg: Number of bytes to jump after last src/dst address of this
    + * chunk and before first src/dst address for next chunk.
    + * Ignored for dst(assumed 0), if dst_inc is true and dst_sgl is false.
    + * Ignored for src(assumed 0), if src_inc is true and src_sgl is false.
    + */
    +struct data_chunk {
    + size_t size;
    + size_t icg;
    +};
    +
    +/**
    + * struct xfer_template - Template to convey DMAC the transfer pattern
    + * and attributes.
    + * @op: The operation to perform on source data before writing it on
    + * to destination address.
    + * @src_start: Bus address of source for the first chunk.
    + * @dst_start: Bus address of destination for the first chunk.
    + * @src_inc: If the source address increments after reading from it.
    + * @dst_inc: If the destination address increments after writing to it.
    + * @src_sgl: If the 'icg' of sgl[] applies to Source (scattered read).
    + * Otherwise, source is read contiguously (icg ignored).
    + * Ignored if src_inc is false.
    + * @dst_sgl: If the 'icg' of sgl[] applies to Destination (scattered write).
    + * Otherwise, destination is filled contiguously (icg ignored).
    + * Ignored if dst_inc is false.
    + * @frm_irq: If the client expects DMAC driver to do callback after each frame.
    + * @numf: Number of frames in this template.
    + * @frame_size: Number of chunks in a frame i.e, size of sgl[].
    + * @sgl: Array of {chunk,icg} pairs that make up a frame.
    + */
    +struct xfer_template {
    + enum dma_transaction_type op;
    + dma_addr_t src_start;
    + dma_addr_t dst_start;
    + bool src_inc;
    + bool dst_inc;
    + bool src_sgl;
    + bool dst_sgl;
    + bool frm_irq;
    + size_t numf;
    + size_t frame_size;
    + struct data_chunk sgl[0];
    +};

    /**
    * enum dma_ctrl_flags - DMA flags to augment operation preparation,
    @@ -432,6 +502,7 @@ struct dma_tx_state {
    * @device_prep_dma_cyclic: prepare a cyclic dma operation suitable for audio.
    * The function takes a buffer of size buf_len. The callback function will
    * be called after period_len bytes have been transferred.
    + * @device_prep_dma_genxfer: Transfer expression in a generic way.
    * @device_control: manipulate all pending operations on a channel, returns
    * zero or error code
    * @device_tx_status: poll for transaction completion, the optional
    @@ -496,6 +567,8 @@ struct dma_device {
    struct dma_async_tx_descriptor *(*device_prep_dma_cyclic)(
    struct dma_chan *chan, dma_addr_t buf_addr, size_t buf_len,
    size_t period_len, enum dma_data_direction direction);
    + struct dma_async_tx_descriptor *(*device_prep_dma_genxfer)(
    + struct dma_chan *chan, struct xfer_template *xt);
    int (*device_control)(struct dma_chan *chan, enum dma_ctrl_cmd cmd,
    unsigned long arg);

    --
    1.7.4.1


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