Pavel Kovalenko has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/28950 )
Change subject: lenovo/x230: introduce FHD variant ......................................................................
Patch Set 8:
Patch Set 8:
I've published the schematic of the latest adapter board here: https://nitrocaster.me/files/X230U_rev6_schematic.pdf Hopefully this will help getting this merged. Let me know what you guys think.
Thanks for sharing! It answers some questions and raises new :)
Most of all, I wonder what exactly U1 does and if it is necessary at all if one controls the firmware. Is it simply translating the BL_CTL_SYS signal to a different PWM frequency? or is it also needed as a buffer? Also, what frequency does it expect on BL_CTL_SYS, if any specific?
And, can you confirm that:
- With the default assembly, one can't control panel power via software.
- But by moving F1 to J1, it would become possible?
U1 acts as a smart translator for EN/PWM signals - whenever EN is high, PWM from the system is translated to the FHD display. Otherwise, EN and PWM are translated high if there's a DC bias on DisplayPort TX lane, which means something is being transmitted to the display. Initially I had an idea that some displays may have PWM brightness regulation, so I also set output PWM frequency to around 1kHz to make it less disgusting. With proper support in the system firmware the adapter board could be completely passive. U1 expects the default 230Hz frequency (or is it 220Hz?), but I believe it should work with 1kHz just as well.
With the default assembly, panel power is sourced directly from VCC3M power rail, so you can't control it. By removing F1 and bridging J1 panel power is switched to VCC3P, which is sourced from a load switch on the motherboard, so you can control it. Note that actually moving F1 to J1 isn't necessary because there's already a fuse on the motherboard.
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Pavel Kovalenko (Code Review)