linux-kernel - Re: [PATCH 1/8] i2c: i2c-bfin-twi: Illegal i2c bus lock upon certain transfer scenarios.

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Date:	Mon, 11 Jun 2012 18:24:47 +0200
From:	Wolfram Sang <w.sang@...gutronix.de>
To:	sonic.zhang@...log.com
Cc:	Ben Dooks <ben-linux@...ff.org>, linux-i2c@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>,
	uclinux-dist-devel@...ckfin.uclinux.org,
	Michael Hennerich <michael.hennerich@...log.com>
Subject: Re: [PATCH 1/8] i2c: i2c-bfin-twi: Illegal i2c bus lock upon certain
 transfer scenarios.

On Wed, May 16, 2012 at 03:20:19PM +0800, sonic.zhang@...log.com wrote:
> From: Michael Hennerich <michael.hennerich@...log.com>
> 
> For transfer counts > 255 bytes i2c-bfin-twi sets the data
> transfer counter DCNT to 0xFF indicating unlimited transfers.
> It then uses a flag iface->manual_stop to manually issue the STOP
> condition, once the required amount of bytes are received.
> 
> We found that on I2C receive operation issuing the STOP condition
> together with a FULL RCV FIFO (2bytes) will cause SDA and SCL be
> constantly driven low.
> 
> Temporary workaround until further investigation:
> Discard the RCV FIFO before issuing the STOP condition.
> 
> Signed-off-by: Michael Hennerich <michael.hennerich@...log.com>
> Signed-off-by: Sonic Zhang <sonic.zhang@...log.com>
> 
> git-svn-id: svn://localhost/svn/linux-kernel/trunk@...1 526b6c2d-f592-4532-a319-5dd88ccb003d

Please remove this line.

> ---
>  drivers/i2c/busses/i2c-bfin-twi.c |    4 ++++
>  1 files changed, 4 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-bfin-twi.c b/drivers/i2c/busses/i2c-bfin-twi.c
> index cdb59e5..e6dd3c9 100644
> --- a/drivers/i2c/busses/i2c-bfin-twi.c
> +++ b/drivers/i2c/busses/i2c-bfin-twi.c
> @@ -131,6 +131,10 @@ static void bfin_twi_handle_interrupt(struct bfin_twi_iface *iface,
>  			iface->transPtr++;
>  			iface->readNum--;
>  		} else if (iface->manual_stop) {
> +			/* Avoid possible bus stall -
> +			 * Flush FIFO before issuing the STOP condition
> +			 */
> +			read_RCV_DATA16(iface);

Please mention that this is currently only a workaround, so people know
there could be still a proper solution.

>  			write_MASTER_CTL(iface,
>  				read_MASTER_CTL(iface) | STOP);
>  		} else if (iface->cur_mode == TWI_I2C_MODE_REPEAT &&
> -- 
> 1.7.0.4
> 
> 

-- 
Pengutronix e.K.                           | Wolfram Sang                |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |

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