I'm looking for sources on the history of Vajrayana, including its origins and development in India and Tibet. I'm not familiar with the area, so anything may come. I already know of Sam van Schaik's EarlyTibet blog and I have Ronald M. Davidson's book "Indian Esoteric Buddhism: A Social History of the Tantric Movement", but basically that's all. I'd especially appreciate good summaries and enlightening essays, but as I've said, any good text is OK.
Note: it is not the religious history I'm interested in but the latest academic research.
"If the Buddha-Nature is seen, there will be no seeing of a nature in any thing."
(Nirvana Sutra, T12n374p521b3; tr. Yamamoto)
"Neither cultivation nor seated meditation — this is the pure Chan of Tathagata."
(Mazu Daoyi, X1321p3b23; tr. Jinhua Jia)
"With sudden enlightenment to Tathagata Chan,
The six paramitas and myriad means are complete within that essence."
(Yongjia Xuanjue, T2014p395c14; tr. from "The Sword of Wisdom")