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

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Message-ID: <CACxGe6u_oubGQKHJh_GOjty5xe1qxj-i18GnKqmi7ANHa3K_Wg@mail.gmail.com>
Date:	Tue, 23 Oct 2012 23:38:41 +0100
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Matt Porter <mporter@...com>
Cc:	Vinod Koul <vinod.koul@...el.com>, Dan Williams <djbw@...com>,
	Chris Ball <cjb@...top.org>,
	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: [RFC PATCH 1/3] dmaengine: add dma_get_channel_caps()

On Fri, Oct 19, 2012 at 3:51 AM, Matt Porter <mporter@...com> wrote:
> Add a dmaengine API to retrieve per channel capabilities.
> Currently, only channel ops and SG segment limitations are
> implemented caps.
>
> The API is optionally implemented by drivers and when
> unimplemented will return a NULL pointer. It is intended
> to be executed after a channel has been requested and, if
> the channel is intended to be used with slave SG transfers,
> then it may only be called after dmaengine_slave_config()
> has executed. The slave driver provides parameters such as
> burst size and address width which may be necessary for
> the dmaengine driver to use in order to properly return SG
> segment limit caps.
>
> Suggested-by: Vinod Koul <vinod.koul@...el.com>
> Signed-off-by: Matt Porter <mporter@...com>

Looks okay to me. Minor comment below...

> +/**
> + * dma_get_channel_caps - flush pending transactions to HW
> + * @chan: target DMA channel
> + * @dir: direction of transfer
> + *
> + * Get the channel-specific capabilities. If the dmaengine
> + * 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)

Looks to me like the returned pointer be a const. Ditto for the
callback prototype in the dma_device structure.

> +{
> +       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);
> --
> 1.7.9.5
>
> --
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-- 
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.
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