Although the terms mianbi (面壁, wall-facing) and biguan (壁觀, wall-vipaśyanā/contemplation), associated with Bodhidharma are interpreted by a number of scholars as some sort of meditative practice involving physical wall gazing, it’s descriptions in newly discovered texts and new translations seem to indicate otherwise. Texts as early as the Dunhuang Long Scroll datable to the early Tang or late texts like the Book of Serenity attribute this practice to Bodhidharma.
The oldest datable text, the Dunhuang mss never describes the practice in detail, nor it is quoted by any historical Zen master. But the meaning of this term as used in the text might be preserved in a long-lost Tibetan translation, in the ninth-century Tibetan treatise Samten Migdrön as Tibetan translators were famous for translating meanings over transliterations.
The original reads ‘If one…. abides in wall-examining (biguan 壁觀),….. no way following after the written teachings—this is mysteriously tallying with principle.”, while The Tibetan reads “If one reverts to the real…. and abides in brightness…..will not follow after the written teachings. This is the quiet of the principle of the real.” So the Tibetan version translates it as ‘brightness’/luminosity’, the in the dzogchen context of this text, the word gsal ba used for biguan likely means original luminosity/enlightenment of mind, nothing sort of physical practice.
The next references are from the Shaoshi liumen 少室六門, the oldest text attributed to Bodhidharma that is quoted by a non-legendary Zen master like Dahui, in his Treasury of the Correct Dharma Eye and his sayings record. Here it is referred to as the mind like a wall
You [should] merely, without(externally): desist from all objective supports; within(internally): have no panting in the mind. With a mind like a wall, you can enter the Way.
Dahui mainly uses this quote, which he calls the upaya words of Bodhidharma, repeatedly in his letters and record, to attack the meditative suppression of thoughts. He also quotes a lost Bodhidhadharma text, also quoted in the Jingde Chuandeng Lu, where the upaya words of mind like a wall is the description of enlightenment. The Anxin famen quoted by Dahui from the same text seems to be a teaching on non-conceptuality.
Similar descriptions about the expedient of no-thought can be found in Huangbo’s record, like,
not till your mind is motionless as wood or stone, will you be on the right road to the Gate.
Zen master Baotang similarly rejects artificial efforts/meditation in his teaching of no-thought.
Complying with birth-and-death is the stain of beings, but depending on stillness is the movement of nirvāṇa. Not complying with birth, not depending on stillness, ‘not entering samādhi, not abiding in seated meditation, there is no-birth and nopractice, and the mind is without loss or gain.