linux-kernel - Re: [PATCH] i2c-designware: Manually set RESTART bit between messages

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Message-ID: <20130703201510.GB2958@katana>
Date:	Wed, 3 Jul 2013 22:15:11 +0200
From:	Wolfram Sang <wsa@...-dreams.de>
To:	Chew Chiau Ee <chiaue.ee.chew@...el.com>
Cc:	linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
	Christian Ruppert <christian.ruppert@...lis.com>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>
Subject: Re: [PATCH] i2c-designware: Manually set RESTART bit between messages


CCing Mika and Christian.

On Fri, Jun 21, 2013 at 03:05:28PM +0800, Chew Chiau Ee wrote:
> From: Chew, Chiau Ee <chiau.ee.chew@...el.com>
> 
> If both IC_EMPTYFIFO_HOLD_MASTER_EN and IC_RESTART_EN are set to 1, the
> Designware I2C controller doesn't generate RESTART unless user specifically
> requests it by setting RESTART bit in IC_DATA_CMD register.
> 
> Since IC_EMPTYFIFO_HOLD_MASTER_EN setting can't be detected from hardware
> register, we must always manually set the restart bit between messages.
> 
> Signed-off-by: Chew, Chiau Ee <chiau.ee.chew@...el.com>

How come restart has worked before? Or did it not?

> ---
>  drivers/i2c/busses/i2c-designware-core.c |   14 ++++++++++++++
>  1 files changed, 14 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-designware-core.c b/drivers/i2c/busses/i2c-designware-core.c
> index 3de5494..9348439 100644
> --- a/drivers/i2c/busses/i2c-designware-core.c
> +++ b/drivers/i2c/busses/i2c-designware-core.c
> @@ -403,6 +403,7 @@ i2c_dw_xfer_msg(struct dw_i2c_dev *dev)
>  	u32 addr = msgs[dev->msg_write_idx].addr;
>  	u32 buf_len = dev->tx_buf_len;
>  	u8 *buf = dev->tx_buf;
> +	bool need_restart = false;
>  
>  	intr_mask = DW_IC_INTR_DEFAULT_MASK;
>  
> @@ -430,6 +431,14 @@ i2c_dw_xfer_msg(struct dw_i2c_dev *dev)
>  			/* new i2c_msg */
>  			buf = msgs[dev->msg_write_idx].buf;
>  			buf_len = msgs[dev->msg_write_idx].len;
> +
> +			/* If both IC_EMPTYFIFO_HOLD_MASTER_EN and
> +			 * IC_RESTART_EN are set, we must manually
> +			 * set restart bit between messages.
> +			 */
> +			if ((dev->master_cfg & DW_IC_CON_RESTART_EN) &&
> +					(dev->msg_write_idx > 0))
> +				need_restart = true;
>  		}
>  
>  		tx_limit = dev->tx_fifo_depth - dw_readl(dev, DW_IC_TXFLR);
> @@ -448,6 +457,11 @@ i2c_dw_xfer_msg(struct dw_i2c_dev *dev)
>  			    buf_len == 1)
>  				cmd |= BIT(9);
>  
> +			if (need_restart) {
> +				cmd |= BIT(10);
> +				need_restart = false;
> +			}
> +
>  			if (msgs[dev->msg_write_idx].flags & I2C_M_RD) {
>  
>  				/* avoid rx buffer overrun */
> -- 
> 1.7.4.4
> 

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