hi,
Got this finally working. Too bad it is almost useless now, we needed it years ago ;-) What is tearsync? It is feature of omapfb driver that allows video playback without tearing effect. This feature is enabled in N8x0 kernel but never was part of Nokia 770 2.6.16 kernel shipped with any firmware. Luckily when first N800 2.6.18 kernel was released there was tearsync support added also in drivers for 770! All that was needed was to backport it to 2.6.16 kernel, right? Well, no. I did but it didn't work.

Only recently I've seen some strange issues with N800's MMC slot when going back to OS2007 and become aware of 'pin multiplexing' issue. Many pins of OMAP chip can be configured in software to have specific signal routed to it and this setting is done in bootloader. So maybe TE pin was simply not enabled? Too bad that any recent OMAP1 datasheet I could find had SoSSI documentation missing. Then I found in Google cache this text "revision D changes: ... removed all references to: ... Specially Optimized Screen Interface (SoSSI) ... deleted SoSSI function from the signal names with the following ball numbers ...". So after additional bit of googling (thanks Serge) and figuring out what all this means the answer is "ball G20, register 4, value 6, offset 6".