[M] Change in coreboot[master]: mb/prodrive/hermes: Prevent SGPIO cross-powering 5V rail
Attention is currently required from: Patrick Rudolph, Christian Walter.
Hello build bot (Jenkins), Patrick Rudolph, Christian Walter,
I'd like you to reexamine a change. Please visit
https://review.coreboot.org/c/coreboot/+/66616
to look at the new patch set (#5).
Change subject: mb/prodrive/hermes: Prevent SGPIO cross-powering 5V rail ......................................................................
mb/prodrive/hermes: Prevent SGPIO cross-powering 5V rail
The PCH's SGPIO pads are connected to a buffer chip that is powered from the always-on +3V3_AUX rail. For some cursed reason, when the SGPIO pads stay configured as SGPIO when a Poseidon system shuts down, voltage from the +3V3_AUX-powered buffer chip will leak into the +5V rail through the SATA backplane. Just pulling the SGPIO pads low before the system powers off stops the +5V rail from being cross-powered.
This issue has only been observed in S5, but it's very likely other sleep states are affected as well. Thus, always pull the SGPIO pins low before entering ACPI S3 or deeper because the power supply will turn off in these states as well.
TEST=Obtain a Poseidon system, verify that the +5V rail is cross-powered after going to S5. We measured 0.17V on our system, but voltages as high as 0.6V were measured on other systems. Verify that unplugging the SGPIO cable going to the SATA backplane results in the +5V rail voltage dropping to 0V, which indicates that the voltage leakage is exclusively coming from the SGPIO and SATA backplane. Finally, make sure that the +5V rail voltage drops to 0V after going into ACPI S5 with this patch applied and the SGPIO cable connected.
Change-Id: Ic872903d5fcdd1c17e02b4c06d5ba29889fbc27d Signed-off-by: Angel Pons th3fanbus@gmail.com --- A src/mainboard/prodrive/hermes/smihandler.c 1 file changed, 55 insertions(+), 0 deletions(-)
git pull ssh://review.coreboot.org:29418/coreboot refs/changes/16/66616/5
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Angel Pons (Code Review)