ppc4xx: Handle i2c stuck on combined xfer

ppc4xx i2c master gets stuck on errors while repeated start is
active. Can be easily reproduced by "i2c md" on an unpopulated
i2c address. There is not stop condition given, scl remains
pulled low.
The only way out seems to be doing a stop manually and then a
soft reset.

Signed-off-by: Dirk Eibach <dirk.eibach@gdsys.cc>
Reviewed-by: Stefan Roese <sr@denx.de>

arch/powerpc/include/asm/ppc4xx-i2c.h

@@ -72,6 +72,8 @@ struct ppc4xx_i2c {
 #define IIC_EXTSTS_XFRA		0x01
 #define IIC_EXTSTS_ICT		0x02
 #define IIC_EXTSTS_LA		0x04
+#define IIC_EXTSTS_BCS_MASK	0x70
+#define IIC_EXTSTS_BCS_FREE	0x40
 
 /* XTCNTLSS Register Bit definition */
 #define IIC_XTCNTLSS_SRST	0x01

drivers/i2c/ppc4xx_i2c.c

@@ -289,6 +289,27 @@ static int _i2c_transfer(struct i2c_adapter *adap,
 			/* Transfer aborted? */
 			if (status & IIC_EXTSTS_XFRA)
 				result = IIC_NOK_XFRA;
+			/* Is bus free?
+			 * If error happened during combined xfer
+			 * IIC interface is usually stuck in some strange
+			 * state without a valid stop condition.
+			 * Brute, but working: generate stop, then soft reset.
+			 */
+			if ((status & IIC_EXTSTS_BCS_MASK)
+			    != IIC_EXTSTS_BCS_FREE){
+				u8 mdcntl = in_8(&i2c->mdcntl);
+
+				/* Generate valid stop condition */
+				out_8(&i2c->xtcntlss, IIC_XTCNTLSS_SRST);
+				out_8(&i2c->directcntl, IIC_DIRCNTL_SCC);
+				udelay(10);
+				out_8(&i2c->directcntl,
+				      IIC_DIRCNTL_SCC | IIC_DIRCNTL_SDAC);
+				out_8(&i2c->xtcntlss, 0);
+
+				ppc4xx_i2c_init(adap, (mdcntl & IIC_MDCNTL_FSM)
+						? 400000 : 100000, 0);
+			}
 		} else if ( status & IIC_STS_PT) {
 			result = IIC_NOK_TOUT;
 		}