linux-kernel - Re: [PATCH v9 3/3] i2c: imx: add DMA support for freescale i2c driver

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Date:	Sat, 8 Nov 2014 18:35:13 +0100
From:	Wolfram Sang <wsa@...-dreams.de>
To:	Yuan Yao <yao.yuan@...escale.com>
Cc:	marex@...x.de, LW@...O-electronics.de, mark.rutland@....com,
	fugang.duan@...escale.com, shawn.guo@...aro.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-i2c@...r.kernel.org
Subject: Re: [PATCH v9 3/3] i2c: imx: add DMA support for freescale i2c driver

Hi,

mostly looking good...

> +#define IMX_I2C_DMA_THRESHOLD	16

Have you guessed or measured this value? A comment about this value
would be nice.

>  
> +struct imx_i2c_dma {
> +	struct dma_chan		*chan_tx;
> +	struct dma_chan		*chan_rx;
> +	struct dma_chan		*chan_using;
> +	struct completion	cmd_complete;
> +	dma_addr_t		dma_buf;
> +	unsigned int		dma_len;
> +	unsigned int		dma_transfer_dir;
> +	unsigned int		dma_data_dir;

Please use proper types as there are things like 'enum
dma_data_direction' and the likes...

> +	dmaengine_submit(txdesc);

This can fail, too. Use dma_submit_error() to check.

> +	result = wait_for_completion_interruptible_timeout(
> +				&i2c_imx->dma->cmd_complete,
> +				msecs_to_jiffies(IMX_I2C_DMA_TIMEOUT));

Have you tested signals extensively? I can't really recommend the
_intrruptible_ here. I don't see any cleaning up to get the bus to a
consistent state again. Most people drop the interruptible sooner or
later.

> +	/* Init DMA config if support*/
> +	i2c_imx_dma_request(i2c_imx, phy_addr);

Make this function void? DMA is optional anyhow.

Thanks,

   Wolfram

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