From: Chang-Ming.Huang@freescale.com
From: Jerry Huang Chang-Ming.Huang@freescale.com
It is sometimes necessary to force the I2C module to become the I2C bus master out of reset and drive SCL(even though SDA may already be driven, which indicates that the bus is busy). This can occur when a system reset does not cause all I2C devices to be reset. Thus, SDA can be driven low by another I2C device while this I2C module is coming out of reset and stays low indefinitely. The following procedure can be used to force this I2C module to generate SCL so that the device driving SDA can finish its transaction.
Signed-off-by: Jerry Huang Chang-Ming.Huang@freescale.com
drivers/i2c/fsl_i2c.c | 18 ++++++++++++++++++ 1 files changed, 18 insertions(+), 0 deletions(-)
diff --git a/drivers/i2c/fsl_i2c.c b/drivers/i2c/fsl_i2c.c index 258be0a..007db70 100644 --- a/drivers/i2c/fsl_i2c.c +++ b/drivers/i2c/fsl_i2c.c @@ -252,6 +252,24 @@ i2c_init(int speed, int slaveadd) writeb(slaveadd << 1, &dev->adr);/* write slave address */ writeb(0x0, &dev->sr); /* clear status register */ writeb(I2C_CR_MEN, &dev->cr); /* start I2C controller */
/* Force I2C module to become bus master which can occure when* a system reset does not cause all I2C devices to be reset */udelay(5);if (readb(&dev->sr) & I2C_SR_MBB) {
You need to the sequence unconditionally, the slave can be stuck without driving SCL.
writeb(I2C_CR_MSTA, &dev->cr);udelay(5);writeb(I2C_CR_MEN | I2C_CR_MSTA, &dev->cr);udelay(5);readb(&dev->dr);udelay(5);writeb(I2C_CR_MEN, &dev->cr);udelay(5);if (readb(&dev->sr) & I2C_SR_MBB)debug("I2C%d: Drive SCL failed\n", i + 1);elsedebug("I2C%d: Drive SCL succeed\n", i + 1);}
The above sequence is different than the kernel version, why?
Kernel version below: static void mpc_i2c_fixup(struct mpc_i2c *i2c) { int k; u32 delay_val = 1000000 / i2c->real_clk + 1;
if (delay_val < 2) delay_val = 2;
for (k = 9; k; k--) { writeccr(i2c, 0); writeccr(i2c, CCR_MSTA | CCR_MTX | CCR_MEN); udelay(delay_val); writeccr(i2c, CCR_MEN); udelay(delay_val << 1); } }