Stephen Warren wrote at Monday, June 06, 2011 11:25 AM: > 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. Ben, Does this patch look OK? I'd categorize it as a bug-fix. Could it go into 3.0? Thanks. > This patch is based on a change previously posted by: Wei Ni <wni@xxxxxxxxxx> > http://www.spinics.net/lists/linux-i2c/msg05437.html > In turned based on internal changes by: Bharat Nihalani > <bnihalani@xxxxxxxxxx> > > 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@xxxxxxxxxx> > --- > 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 4d93196..fb3b4f8 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 | > -- > 1.7.0.4 -- nvpublic -- To unsubscribe from this list: send the line "unsubscribe linux-i2c" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
