[RFC][PATCH v6 0/5] drm/panic: Add a drm panic handler

[Jocelyn Falempe]

drm/panic: Add a drm panic handler

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 with simpledrm and mgag200, 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)
 
v4:
 * Fully support all simpledrm formats using drm conversion helpers
 * Rename dpanic_* to drm_panic_*, and have more coherent function name.
   (Thomas Zimmermann)
 * Use drm_fb_r1_to_32bit for fonts (Thomas Zimmermann)
 * Remove the default y to DRM_PANIC config option (Thomas Zimmermann)
 * Add foreground/background color config option
 * Fix the bottom lines not painted if the framebuffer height
   is not a multiple of the font height.
 * Automatically register the driver to drm_panic, if the function
   get_scanout_buffer() exists. (Thomas Zimmermann)
 * Add mgag200 support.
 
v5:
 * Change the drawing API, use drm_fb_blit_from_r1() to draw the font.
   (Thomas Zimmermann)
 * Also add drm_fb_fill() to fill area with background color.
 * Add draw_pixel_xy() API for drivers that can't provide a linear buffer.
 * Add a flush() callback for drivers that needs to synchronize the buffer.
 * Add a void *private field, so drivers can pass private data to
   draw_pixel_xy() and flush(). 
 * Add ast support.
 * Add experimental imx/ipuv3 support, to test on an ARM hw. (Maxime Ripard)

v6:
 * Fix sparse and __le32 warnings
 * Drop the IMX/IPUV3 experiment, it was just to show that it works also on ARM devices.

With mgag200 support, I was able to test that the xrgb8888 to rgb565 conversion is working.

IMX/IPUV3 support is not complete, I wasn't able to have etnaviv working on my board.
But it shows that it can still work on ARM with DMA buffer in this case.

Best regards,

Jocelyn Falempe (5):
  drm/format-helper: Add drm_fb_blit_from_r1 and drm_fb_fill
  drm/panic: Add a drm panic handler
  drm/simpledrm: Add drm_panic support
  drm/mgag200: Add drm_panic support
  drm/ast: Add drm_panic support

 drivers/gpu/drm/Kconfig               |  22 ++
 drivers/gpu/drm/Makefile              |   1 +
 drivers/gpu/drm/ast/ast_drv.c         |  29 +-
 drivers/gpu/drm/drm_drv.c             |   8 +
 drivers/gpu/drm/drm_format_helper.c   | 431 +++++++++++++++++++++-----
 drivers/gpu/drm/drm_panic.c           | 368 ++++++++++++++++++++++
 drivers/gpu/drm/mgag200/mgag200_drv.c |  25 ++
 drivers/gpu/drm/tiny/simpledrm.c      |  15 +
 include/drm/drm_drv.h                 |  21 ++
 include/drm/drm_format_helper.h       |   9 +
 include/drm/drm_panic.h               |  96 ++++++
 11 files changed, 942 insertions(+), 83 deletions(-)
 create mode 100644 drivers/gpu/drm/drm_panic.c
 create mode 100644 include/drm/drm_panic.h


base-commit: d0b3c318e04cc6c4e2a3c30ee0f6f619aa8d0db5
-- 
2.42.0