[U-Boot] [PATCH] i2c: fix SDA contention in read_byte()

[Reinhard Meyer]

Andrew Dyer wrote:
> NAK.
>
> I2C_TRISTATE is supposed to be persistent until I2C_ACTIVE is called,
> so in the original code it should still be in effect when I2C_SDA(1)
> is executed and there should be no contention.  This patch causes the
> code to actively drive SDA high at the same time the addressed device
> might be driving it low, causing contention until the I2C_TRISTATE
> takes effect.
>   
Right.
Whenever possible by the hardware, I make I2C_SDA/SCL(1) do a tri-state and
I2C_TRISTATE and I2C_ACTIVE are empty.
> In some sense the code is misleadingly written, as it is not allowed
> in the spec to actively drive a '1' on the bus, a chip is only
> supposed to drive 'z' or '0', and the platform is supposed to provide
> the pullup current.  This comes more into play if the i2c bus supports
> clock stretching or arbitration among multiple masters.
>   
I might point out that the soft I2C as it is does not support clock 
stretching. Unless you
add the wait for SCL high into I2C_SCL(1) yourself.

Reinhard