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

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Message-ID: <d1decb2e-ce22-47db-9e17-2492364e5886@suse.de>
Date: Tue, 25 Nov 2025 14:10:55 +0100
From: Thomas Zimmermann <tzimmermann@...e.de>
To: simona@...ll.ch, airlied@...il.com, alexander.deucher@....com,
 christian.koenig@....com, lyude@...hat.com, dakr@...nel.org, deller@....de,
 mripard@...nel.org, maarten.lankhorst@...ux.intel.com,
 jason.wessel@...driver.com, danielt@...nel.org, dianders@...omium.org
Cc: dri-devel@...ts.freedesktop.org, amd-gfx@...ts.freedesktop.org,
 nouveau@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
 linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/5] drm: Remove remaining support for kdb



Am 25.11.25 um 13:52 schrieb Thomas Zimmermann:
> Remove the rest of the kbd support from DRM. Driver support has been

s/kbd/kdb/g  as in 'kernel debugger'

> 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)