linux-kernel - Re: [PATCH 2/5] dmaengine: Add support for custom data mapping

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Date:   Sun, 18 Dec 2016 21:56:02 +0530
From:   Vinod Koul <vinod.koul@...el.com>
To:     Abhishek Sahu <absahu@...eaurora.org>
Cc:     dan.j.williams@...el.com, andy.gross@...aro.org,
        stanimir.varbanov@...aro.org, mcgrof@...e.com,
        okaya@...eaurora.org, pramod.gurav@...aro.org, arnd@...db.de,
        linux-kernel@...r.kernel.org, dmaengine@...r.kernel.org,
        linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH 2/5] dmaengine: Add support for custom data mapping

On Thu, Dec 15, 2016 at 03:25:52PM +0530, Abhishek Sahu wrote:
> The current DMA APIs only support SGL or data in generic format.
> The QCA BAM DMA engine data cannot be mapped with already
> available APIs due to following reasons.
> 
> 1. The QCA BAM DMA engine uses custom flags which cannot be
>    mapped with generic DMA engine flags.
> 2. Some peripheral driver like QCA QPIC NAND/LCD requires to
>    set specific flags (Like NWD, EOT) for some of the descriptors
>    in scatter gather list. The already available mapping APIs take
>    flags parameter in API itself and there is no support for
>    passing DMA specific flags for each SGL entry.
> 
> Now this patch adds the support for making the DMA descriptor from
> custom data with new DMA mapping function prep_dma_custom_mapping.
> The peripheral driver will pass the custom data in this function and
> DMA engine driver will form the descriptor according to its own
> logic. In future, this API can be used by any other DMA engine
> drivers also which are unable to do DMA mapping with already
> available API’s.
> 
> Signed-off-by: Abhishek Sahu <absahu@...eaurora.org>
> ---
>  include/linux/dmaengine.h | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
> index cc535a4..6324c1f 100644
> --- a/include/linux/dmaengine.h
> +++ b/include/linux/dmaengine.h
> @@ -692,6 +692,8 @@ struct dma_filter {
>   *	be called after period_len bytes have been transferred.
>   * @device_prep_interleaved_dma: Transfer expression in a generic way.
>   * @device_prep_dma_imm_data: DMA's 8 byte immediate data to the dst address
> + * @device_prep_dma_custom_mapping: prepares a dma operation from dma driver
> + *	specific custom data
>   * @device_config: Pushes a new configuration to a channel, return 0 or an error
>   *	code
>   * @device_pause: Pauses any transfer happening on a channel. Returns
> @@ -783,6 +785,9 @@ struct dma_device {
>  	struct dma_async_tx_descriptor *(*device_prep_dma_imm_data)(
>  		struct dma_chan *chan, dma_addr_t dst, u64 data,
>  		unsigned long flags);
> +	struct dma_async_tx_descriptor *(*device_prep_dma_custom_mapping)(
> +		struct dma_chan *chan, void *data,
> +		unsigned long flags);

This needs a discussion. Why do you need to add a new API for framework.

What are NWD and EOT flags, cna you details out the flags?

-- 
~Vinod