linux-kernel - RE: [PATCH v7 1/2] i2c: imx: add DMA support for freescale i2c driver

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Message-ID: <c10c1960255e4dbca2a281b995290c6d@BL2PR03MB338.namprd03.prod.outlook.com>
Date:	Fri, 5 Sep 2014 10:32:40 +0000
From:	Yao Yuan <yao.yuan@...escale.com>
To:	Marek Vasut <marex@...x.de>
CC:	"wsa@...-dreams.de" <wsa@...-dreams.de>,
	"LW@...o-electronics.de" <LW@...o-electronics.de>,
	"mark.rutland@....com" <mark.rutland@....com>,
	"fugang.duan@...escale.com" <fugang.duan@...escale.com>,
	"shawn.guo@...aro.org" <shawn.guo@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>
Subject: RE: [PATCH v7 1/2] i2c: imx: add DMA support for freescale i2c driver

On Thursday, September 04, 2014 10:39 PM, Marek Vasut wrote:
> On Wednesday, August 13, 2014 at 11:46:54 AM, Yuan Yao wrote:
> > Add dma support for i2c. This function depend on DMA driver.
> > You can turn on it by write both the dmas and dma-name properties in
> > dts node. DMA is optional, even DMA request unsuccessfully, i2c can
> > also work well.
> >
> > Signed-off-by: Yuan Yao <yao.yuan@...escale.com>
> 
> [...]
> 
> > +/* Enable DMA if transfer byte size is bigger than this threshold.
> > + * As the hardware request, it must bigger than 4.
> 
> The comment is unclear, just by reading it, I have no clue what are the
> units for this value. I can guess those would be bytes, but it would be a
> good idea to be explicit.
> 
> Also, wasn't kernel comment style starting with leading /* , with the
> text starting only on the next line ?
> 

[Yuan Yao] Thanks for your review. I will correct it in the next version.

> > + */
> > +#define IMX_I2C_DMA_THRESHOLD	16
> > +#define IMX_I2C_DMA_TIMEOUT	1000
> > +
> 
> [...]
> 
> > +static int i2c_imx_dma_write(struct imx_i2c_struct *i2c_imx,
> > +					struct i2c_msg *msgs)
> > +{
> > +	int result;
> > +	unsigned int temp = 0;
> > +	unsigned long orig_jiffies = jiffies;
> > +	struct imx_i2c_dma *dma = i2c_imx->dma;
> > +	struct device *dev = &i2c_imx->adapter.dev;
> > +
> > +	dev_dbg(dev, "<%s> write slave address: addr=0x%x\n",
> > +		__func__, msgs->addr << 1);
> > +
> > +	reinit_completion(&i2c_imx->dma->cmd_complete);
> > +	dma->chan_using = dma->chan_tx;
> > +	dma->dma_transfer_dir = DMA_MEM_TO_DEV;
> > +	dma->dma_data_dir = DMA_TO_DEVICE;
> > +	dma->dma_len = msgs->len - 1;
> > +	result = i2c_imx_dma_xfer(i2c_imx, msgs);
> > +	if (result)
> > +		return result;
> > +
> > +	temp = imx_i2c_read_reg(i2c_imx, IMX_I2C_I2CR);
> > +	temp |= I2CR_DMAEN;
> > +	imx_i2c_write_reg(temp, i2c_imx, IMX_I2C_I2CR);
> > +
> > +	/*
> > +	 * Write slave address.
> > +	 * The first byte muse be transmitted by the CPU.
> > +	 */
> > +	imx_i2c_write_reg(msgs->addr << 1, i2c_imx, IMX_I2C_I2DR);
> > +	result = wait_for_completion_interruptible_timeout(
> > +				&i2c_imx->dma->cmd_complete,
> > +				msecs_to_jiffies(IMX_I2C_DMA_TIMEOUT));
> > +	if (result <= 0) {
> > +		dmaengine_terminate_all(dma->chan_using);
> > +		if (result)
> > +			return result;
> > +		else
> > +			return -ETIMEDOUT;
> 
> Shouldn't you force-disable the DMA here somehow (like unsetting
> I2CR_DMAEN bit), if it failed or timed out?

[Yuan Yao] Yes, I put the code for force-disable DMA in i2c_imx_start().
In order to make sure any DMA error will not effect the I2C.
It seems almost the same as put the code here, how about your think?

Thanks!

> > +	}
> > +
> > +	/* Waiting for Transfer complete. */
> > +	while (1) {
> > +		temp = imx_i2c_read_reg(i2c_imx, IMX_I2C_I2SR);
> > +		if (temp & I2SR_ICF)
> > +			break;
> > +		if (time_after(jiffies, orig_jiffies +
> > +				msecs_to_jiffies(IMX_I2C_DMA_TIMEOUT))) {
> > +			dev_dbg(&i2c_imx->adapter.dev, "<%s> Timeout\n",
> > +				__func__);
> > +			return -ETIMEDOUT;
> > +		}
> > +		schedule();
> > +	}
> > +
> > +	temp = imx_i2c_read_reg(i2c_imx, IMX_I2C_I2CR);
> > +	temp &= ~I2CR_DMAEN;
> > +	imx_i2c_write_reg(temp, i2c_imx, IMX_I2C_I2CR);
> > +
> > +	/* The last data byte must be transferred by the CPU. */
> > +	imx_i2c_write_reg(msgs->buf[msgs->len-1],
> > +				i2c_imx, IMX_I2C_I2DR);
> > +	result = i2c_imx_trx_complete(i2c_imx);
> > +	if (result)
> > +		return result;
> > +
> > +	result = i2c_imx_acked(i2c_imx);
> > +	if (result)
> > +		return result;
> > +
> > +	return 0;
> > +}
> [...]
> 
> Thanks!
--
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