[PATCH v9 0/9] drm/panic: Add a drm panic handler

[Jocelyn Falempe]

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, mgag200, ast, and imx.

To test it, make sure you're using one of the supported driver, and trigger a panic:
echo c > /proc/sysrq-trigger

or you can enable CONFIG_DRM_PANIC_DEBUG and echo 1 > /sys/kernel/debug/dri/0/drm_panic_plane_0


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.

v7:
 * Add a check to see if the 4cc format is supported by drm_panic.
 * Add a drm/plane helper to loop over all visible primary buffer,
   simplifying the get_scanout_buffer implementations
 * Add a generic implementation for drivers that uses drm_fb_dma. (Maxime Ripard)
 * Add back the IMX/IPUV3 support, and use the generic implementation. (Maxime Ripard)

v8:
 * Directly register each plane to the panic notifier (Sima)
 * Replace get_scanout_buffer() with set_scanout_buffer() to simplify
   the locking. (Thomas Zimmermann)
 * Add a debugfs entry, to trigger the drm_panic without a real panic (Sima)
 * Fix the drm_panic Documentation, and include it in drm-kms.rst

v9:
 * Revert to using get_scanout_buffer() (Sima)
 * Move get_scanout_buffer() and panic_flush() to the plane helper
   functions (Thomas Zimmermann)
 * Register all planes with get_scanout_buffer() to the panic notifier
 * Use drm_panic_lock() to protect against race (Sima)
 * Create a debugfs file for each plane in the device's debugfs
   directory. This allows to test for each plane of each GPU
   independently.

Daniel Vetter (1):
  drm/panic: Add drm panic locking

Jocelyn Falempe (8):
  drm/format-helper: Add drm_fb_blit_from_r1 and drm_fb_fill
  drm/panic: Add a drm panic handler
  drm/panic: Add debugfs entry to test without triggering panic.
  drm/fb_dma: Add generic get_scanout_buffer() for drm_panic
  drm/simpledrm: Add drm_panic support
  drm/mgag200: Add drm_panic support
  drm/imx: Add drm_panic support
  drm/ast: Add drm_panic support

 Documentation/gpu/drm-kms.rst            |  12 +
 drivers/gpu/drm/Kconfig                  |  32 ++
 drivers/gpu/drm/Makefile                 |   1 +
 drivers/gpu/drm/ast/ast_mode.c           |  18 +
 drivers/gpu/drm/drm_atomic_helper.c      |   3 +
 drivers/gpu/drm/drm_drv.c                |   5 +
 drivers/gpu/drm/drm_fb_dma_helper.c      |  47 +++
 drivers/gpu/drm/drm_format_helper.c      | 432 ++++++++++++++++++-----
 drivers/gpu/drm/drm_panic.c              | 360 +++++++++++++++++++
 drivers/gpu/drm/drm_plane.c              |   1 +
 drivers/gpu/drm/imx/ipuv3/ipuv3-plane.c  |  11 +-
 drivers/gpu/drm/mgag200/mgag200_drv.h    |   7 +-
 drivers/gpu/drm/mgag200/mgag200_mode.c   |  18 +
 drivers/gpu/drm/tiny/simpledrm.c         |  16 +
 include/drm/drm_fb_dma_helper.h          |   4 +
 include/drm/drm_format_helper.h          |   9 +
 include/drm/drm_mode_config.h            |  10 +
 include/drm/drm_modeset_helper_vtables.h |  37 ++
 include/drm/drm_panic.h                  | 151 ++++++++
 include/drm/drm_plane.h                  |   5 +
 20 files changed, 1096 insertions(+), 83 deletions(-)
 create mode 100644 drivers/gpu/drm/drm_panic.c
 create mode 100644 include/drm/drm_panic.h


base-commit: f89632a9e5fa6c4787c14458cd42a9ef42025434
-- 
2.43.2