tree 23c371ef09eb7faa351aa55c455745eaa85007ae
parent ba9ad2af7019956b990ad654c56da5bac1e8b71b
author Jarkko Nikula <jarkko.nikula@linux.intel.com> 1475154299 +0300
committer Wolfram Sang <wsa@the-dreams.de> 1477390149 +0200

i2c: designware: Avoid aborted transfers with fast reacting I2C slaves

I2C DesignWare may abort transfer with arbitration lost if I2C slave pulls
SDA down quickly after falling edge of SCL. Reason for this is unknown but
after trial and error it was found this can be avoided by enabling non-zero
SDA RX hold time for the receiver.

By the specification SDA RX hold time extends incoming SDA low to high
transition by n * ic_clk cycles but only when SCL is high. However it
seems to help avoid above faulty arbitration lost error.

Bits 23:16 in IC_SDA_HOLD register define the SDA RX hold time for the
receiver. Be conservative and enable 1 ic_clk cycle long hold time in
case boot firmware hasn't set it up.

Reported-by: Jukka Laitinen <jukka.laitinen@intel.com>
Signed-off-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Tested-by: Jukka Laitinen <jukka.laitinen@intel.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>