[S] Change in coreboot[master]: mb/clevo/l140mu: work around PECI staying high when idle, blocking s0ix

[Michael Niewöhner (Code Review)]

Attention is currently required from: Felix Singer, Michał Żygowski, Tim Wawrzynczak, Michał Kopeć.

Hello Felix Singer, build bot (Jenkins), Michał Żygowski, Tim Wawrzynczak, Michał Kopeć, Angel Pons,

I'd like you to reexamine a change. Please visit

https://review.coreboot.org/c/coreboot/+/68794

to look at the new patch set (#10).

Change subject: mb/clevo/l140mu: work around PECI staying high when idle, blocking s0ix
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mb/clevo/l140mu: work around PECI staying high when idle, blocking s0ix

According to Intel doc# 575683 the PECI bus should be low when idle and
is pulled up by clients with strong drive. However, for unknown reasons
the bus stays high on this board, blocking s0ix entry.

The PECI reference schematic in the ASPEED AST2400 BMC datasheet
(actually not related to this board) says that a pull-down is *required*
for the idle state.

This might be just a requirement of this BMC, since this is nowhere
documented in Intel datasheets, schematics or elsewhere. However,
configuring a weak pull-down (20 k) on the PECI pad indeed solves this
problem for now.

Change-Id: I85193000af67cd2c0465bdbb58cdd51b68fd5b4f
Signed-off-by: Michael Niewöhner 
---
M src/mainboard/clevo/tgl-u/variants/l140mu/gpio.c
1 file changed, 27 insertions(+), 0 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/94/68794/10