Subject: [PATCH 1/6] dmaengine: Add fly-by transfer flag to slave configuration structure

From: [email-masked] (Vinod Koul)
Date: Fri, 2 May 2014 21:16:34 +0530

On Tue, Apr 15, 2014 at 05:13:32PM +0200, Laurent Pinchart wrote:
> Fly-by transfer mode cuts down the number of bus transactions by letting
> the slave drive or latch the memory data bus during memory transactions
??            ^^^^^^^^^^^
> instead of performing a dedicated transaction to read data from or write
/								^^^^
> data to the slave.
> 
> Support for fly-by mode by adding a new flag field to struct
> dma_slave_config.
> 
> Signed-off-by: Laurent Pinchart <[email-masked]>
> ---
>  include/linux/dmaengine.h | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
> index c5c92d5..ae99153 100644
> --- a/include/linux/dmaengine.h
> +++ b/include/linux/dmaengine.h
> @@ -304,6 +304,17 @@ enum dma_slave_buswidth {
>  };
>  
>  /**
> + * enum dma_slave_flags - DMA slave configuration flags
> + * @DMA_SLAVE_FLAG_FLY_BY - perform DMA transfers for the slave in fly-by mode.
> + *   Instead of performing a bus transaction to read (write) data from (to) the
> + *   slave, let the slave drive (latch) the memory bus data signals during the
> + *   memory write (read) transaction.
> + */
> +enum dma_slave_flags {
> +	DMA_SLAVE_FLAG_FLY_BY = (1 << 0),
> +};
> +
> +/**
>   * struct dma_slave_config - dma slave channel runtime config
>   * @direction: whether the data shall go in or out on this slave
>   * channel, right now. DMA_MEM_TO_DEV and DMA_DEV_TO_MEM are
> @@ -333,6 +344,7 @@ enum dma_slave_buswidth {
>   * @slave_id: Slave requester id. Only valid for slave channels. The dma
>   * slave peripheral will have unique id as dma requester which need to be
>   * pass as slave config.
> + * @flags: DMA slave flags, a combination of enum dma_slave_flags flags.
>   *
>   * 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.
> @@ -361,6 +373,7 @@ struct dma_slave_config {
>  	u32 dst_maxburst;
>  	bool device_fc;
>  	unsigned int slave_id;
> +	u32 flags;
>  };
I am not sure about this. Should we have a generic flag for this or just add a
bool for fly_by mode?

Suggestions?

-- 
~Vinod