linux-kernel - [PATCH v2] i2c-bfin-twi: handle faulty slave devices better

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Message-Id: <1273505624-30920-1-git-send-email-vapier@gentoo.org>
Date:	Mon, 10 May 2010 11:33:44 -0400
From:	Mike Frysinger <vapier@...too.org>
To:	linux-i2c@...r.kernel.org, Ben Dooks <ben-linux@...ff.org>
Cc:	uclinux-dist-devel@...ckfin.uclinux.org,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michael Hennerich <michael.hennerich@...log.com>
Subject: [PATCH v2] i2c-bfin-twi: handle faulty slave devices better

From: Michael Hennerich <michael.hennerich@...log.com>

Faulty slave devices might drive SDA low after a transfer finishes.  So,
when this scenario is detected, have the master generate up to 9 extra
clocks until the SDA is properly released.

Signed-off-by: Michael Hennerich <michael.hennerich@...log.com>
Signed-off-by: Mike Frysinger <vapier@...too.org>
---
v2
	- fix typo in comment pointed out by Ben
	- use 9 clocks rather than 8 to cover a possible NACK pointed out by Michael

 drivers/i2c/busses/i2c-bfin-twi.c |   22 ++++++++++++++++++++++
 1 files changed, 22 insertions(+), 0 deletions(-)

diff --git a/drivers/i2c/busses/i2c-bfin-twi.c b/drivers/i2c/busses/i2c-bfin-twi.c
index fb26e5c..1ee9d5a 100644
--- a/drivers/i2c/busses/i2c-bfin-twi.c
+++ b/drivers/i2c/busses/i2c-bfin-twi.c
@@ -20,6 +20,7 @@
 #include <linux/completion.h>
 #include <linux/interrupt.h>
 #include <linux/platform_device.h>
+#include <linux/delay.h>
 
 #include <asm/blackfin.h>
 #include <asm/portmux.h>
@@ -159,6 +160,27 @@ static void bfin_twi_handle_interrupt(struct bfin_twi_iface *iface,
 		if (mast_stat & BUFWRERR)
 			dev_dbg(&iface->adap.dev, "Buffer Write Error\n");
 
+		/* Faulty slave devices, may drive SDA low after a transfer
+		 * finishes. To release the bus this code generates up to 9
+		 * extra clocks until SDA is released.
+		 */
+
+		if (read_MASTER_STAT(iface) & SDASEN) {
+			int cnt = 9;
+			do {
+				write_MASTER_CTL(iface, SCLOVR);
+				udelay(6);
+				write_MASTER_CTL(iface, 0);
+				udelay(6);
+			} while ((read_MASTER_STAT(iface) & SDASEN) && cnt--);
+
+			write_MASTER_CTL(iface, SDAOVR | SCLOVR);
+			udelay(6);
+			write_MASTER_CTL(iface, SDAOVR);
+			udelay(6);
+			write_MASTER_CTL(iface, 0);
+		}
+
 		/* If it is a quick transfer, only address without data,
 		 * not an err, return 1.
 		 */
-- 
1.7.1

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