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| author | Stephen Warren <swarren@nvidia.com> | 2011-06-06 11:25:19 -0600 |
|---|---|---|
| committer | Ben Dooks <ben-linux@fluff.org> | 2011-06-27 23:03:42 +0100 |
| commit | 5afa9d35782890e8fbd972f12ee5183ba5feb81d (patch) | |
| tree | b34ed30d274eaef7666b98f159d59e80b4c8a8f5 /drivers/i2c/busses | |
| parent | af4087e0e682df12bdffec5cfafc2fec9208716e (diff) | |
| download | linux-5afa9d35782890e8fbd972f12ee5183ba5feb81d.tar.gz linux-5afa9d35782890e8fbd972f12ee5183ba5feb81d.tar.bz2 linux-5afa9d35782890e8fbd972f12ee5183ba5feb81d.zip | |
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>
Diffstat (limited to 'drivers/i2c/busses')
| -rw-r--r-- | drivers/i2c/busses/i2c-tegra.c | 8 |
1 files changed, 7 insertions, 1 deletions
diff --git a/drivers/i2c/busses/i2c-tegra.c b/drivers/i2c/busses/i2c-tegra.c index 4d9319665e32..fb3b4f8f8152 100644 --- a/drivers/i2c/busses/i2c-tegra.c +++ b/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 | |