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Thomas Zimmermann a22461edda drm/radeon: Do not implement mode_set_base_atomic callback 
Remove the implementation of the CRTC helper mode_set_base_atomic
from radeon. It pretends to provide mode setting for kdb debugging,
but has been broken for some time.

Kdb output has been supported only for non-atomic mode setting since
commit 9c79e0b1d0 ("drm/fb-helper: Give up on kgdb for atomic drivers")
from 2017.

While radeon provides non-atomic mode setting, kdb assumes that the GEM
buffer object is at a fixed location in video memory. This assumption
currently blocks radeon from converting to generic fbdev emulation.
Fbdev-ttm helpers use a shadow buffer with a movable GEM buffer object.
Triggering kdb does therefore not update the display.

Another problem is that the current implementation does not handle
USB keyboard input. Therefore a serial terminal is required. Then when
continuing from the debugger, radeon fails with an error:

[7]kdb> go
[   40.345523][    C7] BUG: scheduling while atomic: bash/1580/0x00110003
[...]
[   40.345613][    C7]  schedule+0x27/0xd0
[   40.345615][    C7]  schedule_timeout+0x7b/0x100
[   40.345617][    C7]  ? __pfx_process_timeout+0x10/0x10
[   40.345619][    C7]  msleep+0x31/0x50
[   40.345621][    C7]  radeon_crtc_load_lut+0x2e4/0xcb0 [radeon 31c1ee785de120fcfd0babcc09babb3770252b4e]
[   40.345698][    C7]  radeon_crtc_gamma_set+0xe/0x20 [radeon 31c1ee785de120fcfd0babcc09babb3770252b4e]
[   40.345760][    C7]  drm_fb_helper_debug_leave+0xd8/0x130
[   40.345763][    C7]  kgdboc_post_exp_handler+0x54/0x70
[...]

and the system hangs.

Support for kdb feels pretty much broken. Hence remove the whole kdb
support from radeon.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Christian König <christian.koenig@amd.com>
Acked-by: Simona Vetter <simona.vetter@ffwll.ch>
Acked-by: Daniel Thompson (RISCstar) <danielt@kernel.org>
Link: https://patch.msgid.link/20251125130634.1080966-4-tzimmermann@suse.de
History 2025-12-02 09:20:36 +01:00
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README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.