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npu2-opencapi: Don't drive reset signal permanently
A problem was found with the way we manage the I2C signal to reset adapters. Skiboot currently always drives the value of the opencapi reset signal. We set the I2C pin for reset in output mode and keep it in output mode permanently. And since the reset signal is inverted, it is explicitly set to high by the I2C controller pretty much all the time. When the opencapi card is powered off, for example on a reboot, actively driving the I2C reset pin to high keeps applying a voltage to part of the FPGA, which can leak current, send the FPGA in a bad state since it's unexpected or even damage the card. To prevent damaging adapters, the recommendation from the hardware team is to switch back the pin to input mode at the end of a reset cycle. There are pull-up resistors on the planar of all the platforms to make sure the reset signal is high "naturally". When the slot is powered off, the reset pin won't be kept high by the i2c controller any more. Signed-off-by: Frederic Barrat <fbarrat@linux.ibm.com> Signed-off-by: Oliver O'Halloran <oohall@gmail.com>
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