What's the purpose of using PNP transistors on I2S bus?

[sidlauskas]

What could be the reason of using these 3 PNP transistors on I2S bus (LRCK, BCK and DATA pins)? On the one side of these transistors there is PCM5102 and on another is Qualcomm's CSR64215 bluetooth chip. I know for sure that this schematic would work even without these transistors, but I'm just curious what could be the real purpose of them in this particular schematic. Thank you!

[Nerull]

Probably to allow the use of a relatively low value pullup resistor without sinking all that current through the QSR64215. Low pullup resistor values allow for faster bus operation.