Re: [RFC] dmaengine/dma_slave: add context parameter to prep_slave_sg callback

[Vinod Koul <vinod.koul@intel.com>]

On Thu, 2012-01-26 at 16:22 -0500, Alexandre Bounine wrote:
> As we agreed during our discussion about adding DMA Engine support for RapidIO
> subsystem, RapidIO and similar clients may benefit from adding an extra context
> parameter to device_prep_slave_sg() callback.
> See https://lkml.org/lkml/2011/10/24/275 for more details.
> 
> Adding the context parameter will allow to pass client/target specific
> information associated with an individual data transfer request.
> 
> In the case of RapidIO support this additional information consists of target
> destination ID and its buffer address (which is not mapped into the local CPU
> memory space). Because a single RapidIO-capable DMA channel may queue data
> transfer requests to different target devices, the per-request configuration
> is required.
> 
> The proposed change eliminates need for new subsystem-specific API.
> Existing DMA_SLAVE clients will ignore the new parameter.
> 
> This RFC only demonstrates the API change and does not include corresponding
> changes to existing DMA_SLAVE clients. Complete set of patches will be provided
> after (if) this API change is accepted.
This looks good to me. But was thinking if we need to add this new
parameter for other slave calls (circular, interleaved, memcpy...)

> 
> Signed-off-by: Alexandre Bounine <alexandre.bounine@idt.com>
> Cc: Jassi Brar <jaswinder.singh@linaro.org>
> Cc: Russell King <rmk@arm.linux.org.uk> 
> Cc: Kumar Gala <galak@kernel.crashing.org>
> Cc: Matt Porter <mporter@kernel.crashing.org>
> Cc: Li Yang <leoli@freescale.com>
> ---
>  include/linux/dmaengine.h |    7 ++++---
>  1 files changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
> index 679b349..79d71bb 100644
> --- a/include/linux/dmaengine.h
> +++ b/include/linux/dmaengine.h
> @@ -575,7 +575,7 @@ struct dma_device {
>  	struct dma_async_tx_descriptor *(*device_prep_slave_sg)(
>  		struct dma_chan *chan, struct scatterlist *sgl,
>  		unsigned int sg_len, enum dma_transfer_direction direction,
> -		unsigned long flags);
> +		unsigned long flags, void *context);
>  	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_transfer_direction direction);
> @@ -607,12 +607,13 @@ static inline int dmaengine_slave_config(struct dma_chan *chan,
>  
>  static inline struct dma_async_tx_descriptor *dmaengine_prep_slave_single(
>  	struct dma_chan *chan, void *buf, size_t len,
> -	enum dma_transfer_direction dir, unsigned long flags)
> +	enum dma_transfer_direction dir, unsigned long flags, void *context)
>  {
>  	struct scatterlist sg;
>  	sg_init_one(&sg, buf, len);
>  
> -	return chan->device->device_prep_slave_sg(chan, &sg, 1, dir, flags);
> +	return chan->device->device_prep_slave_sg(chan, &sg, 1, dir, flags,
> +						  context);
>  }
>  
>  static inline int dmaengine_terminate_all(struct dma_chan *chan)


-- 
~Vinod