[Skiboot] [PATCH] npu2-opencapi: Don't drive reset signal permanently

[Andrew Donnellan]

On 6/2/20 3:59 am, Frederic Barrat wrote:
> 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 at linux.ibm.com>

This looks like it should be Cc'd to stable?

-- 
Andrew Donnellan              OzLabs, ADL Canberra
ajd at linux.ibm.com             IBM Australia Limited