i2c-bfin-twi: handle faulty slave devices better

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@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>

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 fb26e5c67515..1ee9d5a31928 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.
                  */