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

[Frederic Barrat]

Le 07/02/2020 à 02:41, Andrew Donnellan a écrit :
> 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?


Good point!
Oliver: do I need to resend?


   Fred