linux-kernel - Re: [PATCH v2 1/3] dmaengine: add dma_get_channel

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Date:	Sun, 20 Jan 2013 04:52:43 -0800
From:	Vinod Koul <vinod.koul@...el.com>
To:	Matt Porter <mporter@...com>
Cc:	Dan Williams <djbw@...com>, Chris Ball <cjb@...top.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	Linux DaVinci Kernel List 
	<davinci-linux-open-source@...ux.davincidsp.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux MMC List <linux-mmc@...r.kernel.org>
Subject: Re: [PATCH v2 1/3] dmaengine: add dma_get_channel_caps()

On Thu, Jan 10, 2013 at 02:07:04PM -0500, Matt Porter wrote:
> +/* struct dmaengine_chan_caps - expose capability of a channel
> + * Note: each channel can have same or different capabilities
> + *
> + * This primarily classifies capabilities into
> + * a) APIs/ops supported
> + * b) channel physical capabilities
> + *
> + * @cap_mask: api/ops capability (DMA_INTERRUPT and DMA_PRIVATE
> + *	       are invalid api/ops and will never be set)
> + * @seg_nr: maximum number of SG segments supported on a SG/SLAVE
> + *	    channel (0 for no maximum or not a SG/SLAVE channel)
> + * @seg_len: maximum length of SG segments supported on a SG/SLAVE
> + *	     channel (0 for no maximum or not a SG/SLAVE channel)
> + */
> +struct dmaengine_chan_caps {
> +	dma_cap_mask_t cap_mask;
> +	int seg_nr;
> +	int seg_len;
> +};
Now am really unclear why we would need direction as argument.

Also, I would add the channel physical capablities like direction, widths,
lengths etc supported.
 
> +/**
> + * dma_get_channel_caps - flush pending transactions to HW
flush pending... ???

> + * driver does not implement per channel capbilities then
> + * NULL is returned.
> + */
> +static inline struct dmaengine_chan_caps
> +*dma_get_channel_caps(struct dma_chan *chan, enum dma_transfer_direction dir)
you need to add this for when CONFIG_DMA_ENGINE is not defined as well.
> +{
> +	if (chan->device->device_channel_caps)
> +		return chan->device->device_channel_caps(chan, dir);
> +	return NULL;
> +}
> +
>  enum dma_status dma_sync_wait(struct dma_chan *chan, dma_cookie_t cookie);
>  #ifdef CONFIG_DMA_ENGINE
>  enum dma_status dma_wait_for_async_tx(struct dma_async_tx_descriptor *tx);
--
~Vinod
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