Re: [RFC] DMAEngine: Define generic transfer request api

[Vinod Koul]

On Sun, 2011-07-24 at 02:01 +0530, Jassi Brar wrote:
> This is an attempt to define an 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. Such cases call for some very condensed api to convey
> pattern of the transfer. This is an attempt at that condensed api.
> 
> The api supports all 4 variants of scatter-gather and contiguous transfer.
> Besides, it could easily represent common operations like
>  	device_prep_dma_{cyclic, memset, memcpy}
and how do you specify if the transfer is cyclic, memset or mempcy...
> and maybe some more that I am not sure of.
> 
> Of course, this api too can't help transfers that don't lend to DMA by
> nature, i.e, scattered tiny read/writes with no periodic pattern. 
For that you use current sg_list :)
> 
> Signed-off-by: Jassi Brar <jaswinder.singh@xxxxxxxxxx>
> ---
>  include/linux/dmaengine.h |   74 +++++++++++++++++++++++++++++++++++++++++++++
>  1 files changed, 74 insertions(+), 0 deletions(-)
> 
> diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
> index eee7add..a6cdb57 100644
> --- a/include/linux/dmaengine.h
> +++ b/include/linux/dmaengine.h
> @@ -74,6 +74,76 @@ 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.
example of ops pls
> + * @src_start: Absolute address of source for the first chunk.
> + * @dst_start: Absolute address of destination for the first chunk.
absolute = bus addr, right, if so bus addr would be a better term
> + * @src_inc: If the source address increments after reading from it.
> + * @dst_inc: If the destination address increments after writing to it.
Is the inc in bytes?
> + * @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.
why not reuse the callback in descriptor for this?
> + * @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,
> @@ -430,6 +500,7 @@ 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_xfer: Transfer expression in 'most' 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
> @@ -494,6 +565,9 @@ 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_xfer)(
> +		struct dma_chan *chan, struct xfer_template *xt,
> +		unsigned long flags);
>  	int (*device_control)(struct dma_chan *chan, enum dma_ctrl_cmd cmd,
>  		unsigned long arg);
>  

Is this coordinated with Sundaram, he was trying similar thing with help
from Linus W?

-- 
~Vinod Koul
Intel Corp.

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