linux-kernel - Re: [PATCH v2 1/2] dmaengine: Add metadata_ops for dma_async_tx

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Message-ID: <20180911073307.GK2634@vkoul-mobl>
Date:   Tue, 11 Sep 2018 13:03:07 +0530
From:   Vinod <vkoul@...nel.org>
To:     Peter Ujfalusi <peter.ujfalusi@...com>
Cc:     dan.j.williams@...el.com, dmaengine@...r.kernel.org,
        linux-kernel@...r.kernel.org, lars@...afoo.de, radheys@...inx.com
Subject: Re: [PATCH v2 1/2] dmaengine: Add metadata_ops for
 dma_async_tx_descriptor

On 30-08-18, 15:19, Peter Ujfalusi wrote:
> The metadata is best described as side band data or parameters traveling
> alongside the data DMAd by the DMA engine. It is data
> which is understood by the peripheral and the peripheral driver only, the
> DMA engine see it only as data block and it is not interpreting it in any
> way.
> 
> The metadata can be different per descriptor as it is a parameter for the
> data being transferred.
> 
> If the DMA supports per descriptor metadata it can implement the attach,
> get_ptr/set_len callbacks.
> 
> Client drivers must only use either attach or get_ptr/set_len to avoid
> misconfiguration.
> 
> Client driver can check if a given metadata mode is supported by the
> channel during probe time with
> dmaengine_is_metadata_mode_supported(chan, DESC_METADATA_CLIENT);
> dmaengine_is_metadata_mode_supported(chan, DESC_METADATA_ENGINE);
> 
> and based on this information can use either mode.
> 
> Wrappers are also added for the metadata_ops.
> 
> To be used in DESC_METADATA_CLIENT mode:
> dmaengine_desc_attach_metadata()
> 
> To be used in DESC_METADATA_ENGINE mode:
> dmaengine_desc_get_metadata_ptr()
> dmaengine_desc_set_metadata_len()
> 
> Signed-off-by: Peter Ujfalusi <peter.ujfalusi@...com>
> ---
>  drivers/dma/dmaengine.c   |  73 ++++++++++++++++++++++++++
>  include/linux/dmaengine.h | 108 ++++++++++++++++++++++++++++++++++++++
>  2 files changed, 181 insertions(+)
> 
> diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
> index f1a441ab395d..53bd1eae23f2 100644
> --- a/drivers/dma/dmaengine.c
> +++ b/drivers/dma/dmaengine.c
> @@ -1306,6 +1306,79 @@ void dma_async_tx_descriptor_init(struct dma_async_tx_descriptor *tx,
>  }
>  EXPORT_SYMBOL(dma_async_tx_descriptor_init);
>  
> +static inline int desc_check_and_set_metadata_mode(
> +	struct dma_async_tx_descriptor *desc, enum dma_desc_metadata_mode mode)
> +{
> +	/* Make sure that the metadata mode is not mixed */
> +	if (!desc->desc_metadata_mode) {
> +		if (dmaengine_is_metadata_mode_supported(desc->chan, mode))
> +			desc->desc_metadata_mode = mode;
> +		else
> +			return -ENOTSUPP;
> +	} else if (desc->desc_metadata_mode != mode) {
> +		return -EINVAL;
> +	}
> +
> +	return 0;
> +}
> +
> +int dmaengine_desc_attach_metadata(struct dma_async_tx_descriptor *desc,
> +				   void *data, size_t len)
> +{
> +	int ret;
> +
> +	if (!desc)
> +		return -EINVAL;
> +
> +	ret = desc_check_and_set_metadata_mode(desc, DESC_METADATA_CLIENT);
> +	if (ret)
> +		return ret;
> +
> +	if (!desc->metadata_ops || !desc->metadata_ops->attach)
> +		return -ENOTSUPP;
> +
> +	return desc->metadata_ops->attach(desc, data, len);
> +}
> +EXPORT_SYMBOL(dmaengine_desc_attach_metadata);

EXPORT_SYMBOL_GPL ?
-- 
~Vinod