[RFC][PATCH v7 0/9] drm/panic: Add a drm panic handler

From: Jocelyn Falempe <jfalempe@redhat.com>
To: dri-devel@lists.freedesktop.org, tzimmermann@suse.de,
	airlied@redhat.com, maarten.lankhorst@linux.intel.com,
	mripard@kernel.org, daniel@ffwll.ch, javierm@redhat.com,
	bluescreen_avenger@verizon.net, noralf@tronnes.org
Cc: gpiccoli@igalia.com, Jocelyn Falempe <jfalempe@redhat.com>
Subject: [RFC][PATCH v7 0/9] drm/panic: Add a drm panic handler
Date: Thu,  4 Jan 2024 17:00:44 +0100	[thread overview]
Message-ID: <20240104160301.185915-1-jfalempe@redhat.com> (raw)

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 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.

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)

Best regards,

Jocelyn Falempe (9):
  drm/format-helper: Add drm_fb_blit_from_r1 and drm_fb_fill
  drm/panic: Add a drm panic handler
  drm/plane: Add drm_for_each_primary_visible_plane macro
  drm/panic: Add drm_panic_is_format_supported()
  drm/fb_dma: Add generic get_scanout_buffer() for drm_panic
  drm/simpledrm: Add drm_panic support
  drm/mgag200: Add drm_panic support
  drm/ast: Add drm_panic support
  drm/imx: Add drm_panic support

 drivers/gpu/drm/Kconfig                  |  23 ++
 drivers/gpu/drm/Makefile                 |   1 +
 drivers/gpu/drm/ast/ast_drv.c            |  26 +-
 drivers/gpu/drm/drm_drv.c                |   8 +
 drivers/gpu/drm/drm_fb_dma_helper.c      |  55 +++
 drivers/gpu/drm/drm_format_helper.c      | 432 ++++++++++++++++++-----
 drivers/gpu/drm/drm_panic.c              | 382 ++++++++++++++++++++
 drivers/gpu/drm/imx/ipuv3/imx-drm-core.c |   2 +
 drivers/gpu/drm/mgag200/mgag200_drv.c    |  22 ++
 drivers/gpu/drm/tiny/simpledrm.c         |  15 +
 include/drm/drm_drv.h                    |  21 ++
 include/drm/drm_fb_dma_helper.h          |   4 +
 include/drm/drm_format_helper.h          |   9 +
 include/drm/drm_panic.h                  | 101 ++++++
 include/drm/drm_plane.h                  |  15 +
 15 files changed, 1033 insertions(+), 83 deletions(-)
 create mode 100644 drivers/gpu/drm/drm_panic.c
 create mode 100644 include/drm/drm_panic.h

base-commit: 50a3c772bd927dd409c484832ddd9f6bf00b7389
-- 
2.43.0