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

Oliver O'Halloran oohall at gmail.com
Mon Feb 17 14:54:58 AEDT 2020

On Fri, Feb 7, 2020 at 7:19 PM Frederic Barrat <fbarrat at linux.ibm.com> wrote:
> 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?

Ask Vasant to pick it up or sent it to the stable list.

Merged as 53408440edb30de7ad18f12db285f15a0863fbc3

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