Re: [PATCH 0/5] drm: Remove remaining support for kdb

Thomas Zimmermann
2025-12-01T16:41:25Z

Series has been acked by Sima via IRC. Patches 4 and 5 have been r-b'ed.

https://people.freedesktop.org/~cbrill/dri-log/?channel=dri-devel&highlight_names=&date=2025-12-01&show_html=true

Am 25.11.25 um 13:52 schrieb Thomas Zimmermann:
> Remove the rest of the kbd support from DRM. Driver support has been
> broken for years without anyone complaining.
>
> Kdb cannot use regular DRM mode setting, so DRM drivers have to
> implement an additional hook to make it work (in theory). As outlined
> by Sima in commit 9c79e0b1d096 ("drm/fb-helper: Give up on kgdb for
> atomic drivers") from 2017, kdb is not compatible with DRM atomic mode
> setting. Non-atomic mode setting meanwhile has become rare.
>
> Only 3 DRM drivers implement the hooks for kdb support. Amdgpu and
> nouveau use non-atomic mode setting on older devices. But both drivers
> have switched to generic fbdev emulation, which isn't compatible with
> kdb. Radeon still runs kdb, but it doesn't work in practice. See the
> commits in this series for details
>
> Therefore remove the remaining support for kdb from the DRM drivers
> and from DRM fbdev emulation. Also remove the hooks from fbdev, as
> there are no fbdev drivers with kdb support.
>
> If we ever want to address kdb support within DRM drivers, a place to
> start would be the scanout buffers used by DRM's panic screen. These
> use the current display mode. They can be written and flushed without
> mode setting involved.
>
> Note: kdb over serial lines is not affected by this series and continues
> to work as before.
>
> Thomas Zimmermann (5):
> drm/amdgpu: Do not implement mode_set_base_atomic callback
> drm/nouveau: Do not implement mode_set_base_atomic callback
> drm/radeon: Do not implement mode_set_base_atomic callback
> drm/fbdev-helper: Remove drm_fb_helper_debug_enter/_leave()
> fbcon: Remove fb_debug_enter/_leave from struct fb_ops
>
> Documentation/process/debugging/kgdb.rst | 28 -----
> drivers/gpu/drm/amd/amdgpu/dce_v10_0.c | 35 ++-----
> drivers/gpu/drm/amd/amdgpu/dce_v6_0.c | 35 ++-----
> drivers/gpu/drm/amd/amdgpu/dce_v8_0.c | 35 ++-----
> drivers/gpu/drm/drm_fb_helper.c | 108 --------------------
> drivers/gpu/drm/nouveau/dispnv04/crtc.c | 24 +----
> drivers/gpu/drm/radeon/atombios_crtc.c | 74 ++++----------
> drivers/gpu/drm/radeon/radeon_legacy_crtc.c | 23 ++---
> drivers/gpu/drm/radeon/radeon_mode.h | 10 +-
> drivers/video/fbdev/core/fbcon.c | 24 -----
> drivers/video/fbdev/core/fbcon.h | 1 -
> include/drm/drm_fb_helper.h | 21 ----
> include/drm/drm_modeset_helper_vtables.h | 23 -----
> include/linux/fb.h | 4 -
> 14 files changed, 63 insertions(+), 382 deletions(-)
>
>
> base-commit: 0a21e96e0b6840d2a4e0b45a957679eeddeb4362

--
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com
GF: Jochen Jaser, Andrew McDonald, Werner Knoblich, (HRB 36809, AG Nürnberg)