David Wu has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/29796 )
Change subject: mb/google/fizz/variants/karma: Clear GPP_B4 when entering S5 ......................................................................
Patch Set 2:
(1 comment)
https://review.coreboot.org/#/c/29796/2//COMMIT_MSG Commit Message:
https://review.coreboot.org/#/c/29796/2//COMMIT_MSG@11 PS2, Line 11: BUG=b:124197348
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See comment3 below. for scenario 2, need setting GPP_B4 to low in S5. Thanks. ================================== Please refer to the attached photos for the power sequence requirement of LG touch screen . scenario 1 : power on Tuning the power sequence by hardware R/C delay as the attached circuit The sequence spec : Vlcd must lead Vusb more than 60 ms .
scenario 2 : power off Need firmware's help to turn off TS power by pulling low the "PCH_TS_EN" pin (GPP_B4) when received "power off" command . The sequence spec : Vlcd must lag Vusb more than 0 ms .
scenario 3: sleep mode/suspend (S3) In order to keep the system can be waked up by touch screen so must let Vusb be kept . The firmware don't need to do anything for touch screen power during s3 .
The waveforms after tuning were attached as well , please have a look . Blue color - Vusb Yellow color - Vlcd