i2c: tegra: Assign unused slave address

On Tegra, we should always use the "new" I2C slave controller, to avoid
issues with the old controller. This was implemented in commit 65a1a0a
"i2c: tegra: Enable new slave mode."

There is currently no driver for the Tegra I2C slave controller upstream.
Additionally, the controller cannot be completely disabled. Instead, we
need to:

a) Set I2C_SL_CNFG_NACK to make the controller automatically NACK any
incoming transactions.

b) The controller's definition of NACK isn't identical to the I2C
protocol's definition. Specifically, it will perform a standard NACK, but
*also* continue to hold the clock line low in expectation of receiving
more data. This can hang the bus, or at least cause transaction timeouts,
if something starts a transaction that matches the controller's slave
address. Since the default address is 0x00, the general call address,
this does occur in practice.

To avoid this, we explicitly program a slave address that is reserved for
future expansion. For current boards, this guarantees the address will
never be used. If a future board ever needs to use this address, we can
add platform data to determine a board-specific safe address. 0xfc is
picked by this patch.

This patch is based on a change previously posted by: Wei Ni <wni@nvidia.com>
http://www.spinics.net/lists/linux-i2c/msg05437.html
In turned based on internal changes by: Bharat Nihalani <bnihalani@nvidia.com>

A semantically equivalent change has been contained in the various
ChromeOS kernels for a while.

I tested this change on top of 3.0-rc2 on Harmony, and interacted with
the WM8903 I2C-based audio codec.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>

drivers/i2c/busses/i2c-tegra.c

@@ -40,8 +40,10 @@
 #define I2C_CNFG_NEW_MASTER_FSM			(1<<11)
 #define I2C_STATUS				0x01C
 #define I2C_SL_CNFG				0x020
+#define I2C_SL_CNFG_NACK			(1<<1)
 #define I2C_SL_CNFG_NEWSL			(1<<2)
 #define I2C_SL_ADDR1				0x02c
+#define I2C_SL_ADDR2				0x030
 #define I2C_TX_FIFO				0x050
 #define I2C_RX_FIFO				0x054
 #define I2C_PACKET_TRANSFER_STATUS		0x058
@@ -337,7 +339,11 @@ static int tegra_i2c_init(struct tegra_i2c_dev *i2c_dev)
 
 	if (!i2c_dev->is_dvc) {
 		u32 sl_cfg = i2c_readl(i2c_dev, I2C_SL_CNFG);
-		i2c_writel(i2c_dev, sl_cfg | I2C_SL_CNFG_NEWSL, I2C_SL_CNFG);
+		sl_cfg |= I2C_SL_CNFG_NACK | I2C_SL_CNFG_NEWSL;
+		i2c_writel(i2c_dev, sl_cfg, I2C_SL_CNFG);
+		i2c_writel(i2c_dev, 0xfc, I2C_SL_ADDR1);
+		i2c_writel(i2c_dev, 0x00, I2C_SL_ADDR2);
+
 	}
 
 	val = 7 << I2C_FIFO_CONTROL_TX_TRIG_SHIFT |