linux-kernel - Re: [PATCH 2/4] i2c-designware: always set the STOP bit after last byte

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Message-ID: <20130117103248.GL10814@arwen.pp.htv.fi>
Date:	Thu, 17 Jan 2013 12:32:48 +0200
From:	Felipe Balbi <balbi@...com>
To:	Mika Westerberg <mika.westerberg@...ux.intel.com>
CC:	<linux-i2c@...r.kernel.org>, Wolfram Sang <w.sang@...gutronix.de>,
	"Ben Dooks (embedded platforms)" <ben-linux@...ff.org>,
	Jean Delvare <khali@...ux-fr.org>, <dirk.brandewie@...il.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/4] i2c-designware: always set the STOP bit after last
 byte

Hi,

On Thu, Jan 17, 2013 at 12:31:05PM +0200, Mika Westerberg wrote:
> If IC_EMPTYFIFO_HOLD_MASTER_EN is set to one, the DesignWare I2C controller
> doesn't generate STOP on the bus when the FIFO is empty. This violates the
> rules of Linux I2C stack as it requires that the STOP is issued once the
> i2c_transfer() is finished.
> 
> However, there is no way to detect this from the hardware registers, so we
> must make sure that the STOP bit is always set once the last byte of the
> last message is transferred.
> 
> This patch is based on the work of Dirk Brandewie.
> 
> Signed-off-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
> ---
>  drivers/i2c/busses/i2c-designware-core.c |   16 ++++++++++++++--
>  1 file changed, 14 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-designware-core.c b/drivers/i2c/busses/i2c-designware-core.c
> index f5258c2..94fd818 100644
> --- a/drivers/i2c/busses/i2c-designware-core.c
> +++ b/drivers/i2c/busses/i2c-designware-core.c
> @@ -413,11 +413,23 @@ i2c_dw_xfer_msg(struct dw_i2c_dev *dev)
>  		rx_limit = dev->rx_fifo_depth - dw_readl(dev, DW_IC_RXFLR);
>  
>  		while (buf_len > 0 && tx_limit > 0 && rx_limit > 0) {
> +			u32 cmd = 0;
> +
> +			/*
> +			 * If IC_EMPTYFIFO_HOLD_MASTER_EN is set we must
> +			 * manually set the stop bit. However, it cannot be
> +			 * detected from the registers so we set it always
> +			 * when writing/reading the last byte.
> +			 */
> +			if (dev->msg_write_idx == dev->msgs_num - 1 &&
> +			    buf_len == 1)
> +				cmd |= BIT(9);
> +
>  			if (msgs[dev->msg_write_idx].flags & I2C_M_RD) {
> -				dw_writel(dev, 0x100, DW_IC_DATA_CMD);
> +				dw_writel(dev, cmd | 0x100, DW_IC_DATA_CMD);
>  				rx_limit--;
>  			} else
> -				dw_writel(dev, *buf++, DW_IC_DATA_CMD);
> +				dw_writel(dev, cmd | *buf++, DW_IC_DATA_CMD);

also need to send STP bit if I2C_M_STOP is set.

-- 
balbi

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