linux-kernel - [PATCH 1/8 v2] i2c: i2c-bfin-twi: Illegal i2c bus lock upon certain transfer scenarios.

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Date:	Wed, 13 Jun 2012 16:22:40 +0800
From:	Sonic Zhang <sonic.adi@...il.com>
To:	Wolfram Sang <w.sang@...gutronix.de>,
	Ben Dooks <ben-linux@...ff.org>
CC:	<linux-i2c@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
	<uclinux-dist-devel@...ckfin.uclinux.org>,
	Michael Hennerich <michael.hennerich@...log.com>,
	Sonic Zhang <sonic.zhang@...log.com>
Subject: [PATCH 1/8 v2] i2c: i2c-bfin-twi: Illegal i2c bus lock upon certain transfer scenarios.

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>
---
 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..33031f0 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) {
+			/* Temporary workaround to avoid possible bus stall -
+			 * Flush FIFO before issuing the STOP condition
+			 */
+			read_RCV_DATA16(iface);
 			write_MASTER_CTL(iface,
 				read_MASTER_CTL(iface) | STOP);
 		} else if (iface->cur_mode == TWI_I2C_MODE_REPEAT &&
-- 
1.7.0.4


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