Umm...
Deep learning is just for "Firmware development" not YOUR each Camera.
OpenCV: Cascade Classifier OpenCV: samples/cpp/facedetect.cpp
for Face detection and Eye-AF, a Trained modeling data is needed. This data is already included in firmware binary file. (and will be any datafile of filesystem in DSLR Flash Memory).
and detection performance(speed,accuracy...) is depend on that modeling data is Well-trained or not.
Trained modeling data is made by (psudo code: ) train(many many face photos) method.
Mr.Wakashiro, Chief of Dev.team for PENTAX K-3 Mark III said "if needed, any firmware may be made for specific purpose like for airplane detection... " on CP+2021. This means same to my opinion.
btw, I'm sure PENTAX may use OpenCV by SC2000, just my think. lol
(Don't trust.
PENTAX never officially said "we use SC2000". lol)