This introduces a new drm panic handler, which displays a message when a panic occurs. So when fbcon is disabled, you can still see a kernel panic.
This is one of the missing feature, when disabling VT/fbcon in the kernel: https://www.reddit.com/r/linux/comments/10eccv9/config_vtn_in_2023/ Fbcon can be replaced by a userspace kms console, but the panic screen must be done in the kernel. This is a proof of concept, and works only with simpledrm, using a new get_scanout_buffer() api To test it, make sure you're using the simpledrm driver, and trigger a panic: echo c > /proc/sysrq-trigger v2: * Use get_scanout_buffer() instead of the drm client API. (Thomas Zimmermann) * Add the panic reason to the panic message (Nerdopolis) * Add an exclamation mark (Nerdopolis) v3: * Rework the drawing functions, to write the pixels line by line and to use the drm conversion helper to support other formats. (Thomas Zimmermann) I only added RGB565 support to show how it would work. Basically I have a buffer of 1 line in xrgb8888, and write the pixels to it. Then I convert it to the destination format in-place (if needed), and finally copy it to the scanout-buffer. So it's straigh forward, and reuse the drm conversion helpers. A few more though: 1) what about gpu with multiple monitor connected ? maybe get_scanout_buffer() could return a list of scanout buffers ? 2) I think for some GPU drivers, there might need a flush_scanout_buffer() function, that should be called after the scanout buffer has been filled ? Best regards, Jocelyn Falempe (3): drm/format-helper: Export drm_fb_xrgb8888_to_rgb565_line drm/panic: Add a drm panic handler drm/simpledrm: Add drm_panic support drivers/gpu/drm/Kconfig | 11 + drivers/gpu/drm/Makefile | 1 + drivers/gpu/drm/drm_drv.c | 3 + drivers/gpu/drm/drm_format_helper.c | 3 +- drivers/gpu/drm/drm_panic.c | 366 ++++++++++++++++++++++++++++ drivers/gpu/drm/tiny/simpledrm.c | 17 ++ include/drm/drm_drv.h | 14 ++ include/drm/drm_format_helper.h | 2 + include/drm/drm_panic.h | 41 ++++ 9 files changed, 457 insertions(+), 1 deletion(-) create mode 100644 drivers/gpu/drm/drm_panic.c create mode 100644 include/drm/drm_panic.h base-commit: 2dde18cd1d8fac735875f2e4987f11817cc0bc2c -- 2.41.0
