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The I2C peripheral on the EC can get confused if there is a very specific kind of noise introduced to the line. This can be manifested by jiggling the battery jack. It gets the I2C into a state where everything seems fine outwardly, but the device refuses to even transmit START bits on the line. It appears that one of the stray pulses on the i2c bus gets the device off set from the actual bytes, leaving it misinterpreting everything and waiting forever. In this case, there is only one way to recover (as you can't directly access these aspects of the internal state) and that is to do a software reset of the i2c peripheral. Here I add some code to check for the condition where the EC was unable to even send a START bit, and do a software reset of the i2c to recover. BUG=chrome-os-partner:13161 TEST=With a faulty-battery-jack-board: Boot board, test that i2c works by running "pmu" on the EC console. Jiggle battery jack repeatedly until errors are displayed on console. Try to run pmu again. Make sure that it recovers gracefully, and do this many times. BRANCH=snow Change-Id: I91b8ef0c6f6079bc63f4a6a1bc91f67d19db9fc0 Signed-off-by: Charlie Mooney <charliemooney@chromium.org> Reviewed-on: https://gerrit.chromium.org/gerrit/32286 Reviewed-by: David Hendricks <dhendrix@chromium.org>