Subject: [PATCH] i2c: designware: prevent early stop on TX FIFO empty

From: [email-masked] (Wolfram Sang)
Date: Wed, 19 Nov 2014 10:21:22 +0100

On Fri, Nov 07, 2014 at 12:10:44PM +0000, Andrew Jackson wrote:
> If the Designware core is configured with IC_EMPTYFIFO_HOLD_MASTER_EN
> set to zero, allowing the TX FIFO to become empty causes a STOP
> condition to be generated on the I2C bus. If the transmit FIFO
> threshold is set too high, an erroneous STOP condition can be
> generated on long transfers - particularly where the interrupt
> latency is extended.
> 
> Signed-off-by: Andrew Jackson <[email-masked]>
> Signed-off-by: Liviu Dudau <[email-masked]>

So, what do other designware users think of this change (nice CC list
BTW, Andrew). Adding Mika, too.

> ---
>  drivers/i2c/busses/i2c-designware-core.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-designware-core.c b/drivers/i2c/busses/i2c-designware-core.c
> index 3c20e4b..e070edd 100644
> --- a/drivers/i2c/busses/i2c-designware-core.c
> +++ b/drivers/i2c/busses/i2c-designware-core.c
> @@ -363,7 +363,7 @@ int i2c_dw_init(struct dw_i2c_dev *dev)
>  	}
>  
>  	/* Configure Tx/Rx FIFO threshold levels */
> -	dw_writel(dev, dev->tx_fifo_depth - 1, DW_IC_TX_TL);
> +	dw_writel(dev, dev->tx_fifo_depth / 2, DW_IC_TX_TL);
>  	dw_writel(dev, 0, DW_IC_RX_TL);
>  
>  	/* configure the i2c master */
> -- 
> 1.7.1
> 
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