Is it possible to have master to master communication via I2C, I have to communicate between Raspberry pi and Attiny 85. I have a problem that I want to send data to raspberrypi when attiny want and not when Raspberrypi wants.
Also, is it possible to use raspberry pi as slave with master as attiny 85.
Is it possible to have master to master communication via I2C
No.
I have to communicate between Raspberry pi and Attiny 85
How about UART communication? The Raspberry Pi and the ATtiny85 are able to do that.
Also, is it possible to use raspberry pi as slave with master as attiny 85.
I can answer the ATtiny 85 side: yes, that's possible. To my knowledge the Raspberry Pi is not able to handle I2C in slave mode but that's a question for a Raspberry Pi forum.