Bodhidharma didn't read Mazu and Daoxin didn't read Joshu. Neither did their contemporaries. And there were a few.
The greta Sage you speak of so lightly in your usual ignorant manner was in fact extremely well educated. After all, he was the third son of a great Brahman King, (although Yáng Xuànzhī's (Yang Hsüan-chih) The Record of the Buddhist Monasteries of Luoyang claim him to be A monk of the Western Region named Bodhidharma, a Persian Central Asian from Persia - page 547).
His education streched from profound insight into Indian martial arts like Angampora / Kalaripayat that later served as a base for his teaching of the Shaolin monks in what was called 18 monks boxing through Gongfu, the latter meaning means Supreme skill from hard work.
Beside being a Buddhist Master (with extensive insight into the various sutras of the time) He was also proficient in the very difficult art of Ayurveda or Ayurvedic medicine, not to forget his deep insight in the Lankavatara sutra , him also being a Lanka Master. He was basically a Polymath of immense proportions.
Lets see what some older literature say about him;
"An Indian Buddhist who went to China, and there formally established the Buddha-Mind School, called also Ch'an and later, in Japan, Zen. Bodhidharma received his name in India from his teacher Panyata,who called him so because of his great knowledge of the Law (dharma or dhamma) or Truth (Bodhi) taught by Buddha. He was originally a kshatriya, son of a king, and became an arhat." -** ZEN Dictionary by ERNEST WOOD (1962 edition).**
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Bodhidharma (Sk.) Deeply learned Indian Bst. who arrived at the Chinese Court in a.d. 520. - A populary dictionary of Buddhism by Christmas Humphreys 1963 edition.