> From: <chang-ming.hu...@freescale.com>
>
> From: Jerry Huang <chang-ming.hu...@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.hu...@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);
> + else
> + debug("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);
}
}
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