[S] Change in coreboot[master]: mb/clevo/l140cu: work around PECI staying high when idle, blocking s0ix

[Michael Niewöhner (Code Review)]

Michael Niewöhner has submitted this change. ( https://review.coreboot.org/c/coreboot/+/68793 )

(

4 is the latest approved patch-set.
No files were changed between the latest approved patch-set and the submitted one.
 )Change subject: mb/clevo/l140cu: work around PECI staying high when idle, blocking s0ix
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mb/clevo/l140cu: 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: Ib5a6b0ad3553c2cf795037d6a1982102bcb04644
Signed-off-by: Michael Niewöhner 
Reviewed-on: https://review.coreboot.org/c/coreboot/+/68793
Reviewed-by: Angel Pons 
Tested-by: build bot (Jenkins) 
---
M src/mainboard/clevo/cml-u/variants/l140cu/gpio.c
1 file changed, 29 insertions(+), 0 deletions(-)

Approvals:
  build bot (Jenkins): Verified
  Angel Pons: Looks good to me, approved

diff --git a/src/mainboard/clevo/cml-u/variants/l140cu/gpio.c b/src/mainboard/clevo/cml-u/variants/l140cu/gpio.c
index fb658dd..258f076 100644
--- a/src/mainboard/clevo/cml-u/variants/l140cu/gpio.c
+++ b/src/mainboard/clevo/cml-u/variants/l140cu/gpio.c
@@ -233,6 +233,9 @@
    PAD_NC(GPP_H21, NONE),
    PAD_NC(GPP_H22, UP_20K),
    PAD_NC(GPP_H23, UP_20K),
+
+	/* ------- GPIO Group CPU ------- */
+	PAD_CFG_NF(PECI_IO, DN_20K, DEEP, NF1),		/* PECI */
 };

void variant_configure_gpios(void)