i2c: tegra: Add de-bounce cycles.

This enables debouncing of the I2C lines. The debounce period is
2 * the debounce register field value, in terms of the I2C block's main
clock. The Tegra TRM indicates that a setting yielding >50nS is
desirable. Hence, a setting of 2 => 4 clocks @ 72MHz => ~55nS.

Signed-off-by: Ken Radtke <kradtke@nvidia.com>
[swarren: Added commit description body,
 Fixed 80-column limit, Reverted file permission change]
Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>

drivers/i2c/busses/i2c-tegra.c

@@ -35,6 +35,7 @@
 #define BYTES_PER_FIFO_WORD 4
 
 #define I2C_CNFG				0x000
+#define I2C_CNFG_DEBOUNCE_CNT_SHIFT		12
 #define I2C_CNFG_PACKET_MODE_EN			(1<<10)
 #define I2C_CNFG_NEW_MASTER_FSM			(1<<11)
 #define I2C_STATUS				0x01C
@@ -328,7 +329,8 @@ static int tegra_i2c_init(struct tegra_i2c_dev *i2c_dev)
 	if (i2c_dev->is_dvc)
 		tegra_dvc_init(i2c_dev);
 
-	val = I2C_CNFG_NEW_MASTER_FSM | I2C_CNFG_PACKET_MODE_EN;
+	val = I2C_CNFG_NEW_MASTER_FSM | I2C_CNFG_PACKET_MODE_EN |
+		(0x2 << I2C_CNFG_DEBOUNCE_CNT_SHIFT);
 	i2c_writel(i2c_dev, val, I2C_CNFG);
 	i2c_writel(i2c_dev, 0, I2C_INT_MASK);
 	clk_set_rate(i2c_dev->clk, i2c_dev->bus_clk_rate * 8);