[BISECTED] 5.14.0-rc4 broke drm/ttm when !CONFIG_DEBUG_FS

From: Mikael Pettersson
Date: Mon Aug 02 2021 - 13:17:08 EST

Booting 5.14.0-rc4 on my box with Radeon graphics breaks with

[drm:radeon_ttm_init [radeon]] *ERROR* failed initializing buffer
object driver(-19).
radeon 0000:01:00.0: Fatal error during GPU init

after which the screen goes black for the rest of kernel boot and
early user-space init.
Once the console login shows up the screen is in some legacy low-res
mode and Xorg can't be started.

A git bisect between v5.14-rc3 (good) and v5.14-rc4 (bad) identified

# first bad commit: [69de4421bb4c103ef42a32bafc596e23918c106f]
drm/ttm: Initialize debugfs from ttm_global_init()

Reverting that from 5.14.0-rc4 gives me a working kernel again.

Note that I have
# CONFIG_DEBUG_FS is not set