On 18/08/2026 14:27, Thomas Zimmermann wrote:
Split DRM's current panic handling into a core and a helper module.
The core is still part of DRM's core library. The panic helpers are
part of DRM's KMS helper module (for now).
The motivation behind this series is to get panic handling's drawing
code out of the DRM core. At some point it should share a single
module with DRM's other drawing and format conversion.
With the series applied, panic hanlding follows DRM's established
design pattern of having a DRM core interface with an dedicated
implementation in each driver. Drivers share common code in helper
modules. For panic handling, the DRM core still contains the panic
entry points, the parameters and the debugfs interface. All drawing
is now located in the panic helpers.
Patches 1 to 4 improve several issues in the current panic code. It
makes sense to fix them before moving the core around.
Patches 5 to 8 put handling of all panic state and locking into a
single place, drm_panic_display_panic_screen(). It is maintained by
panic handling's DRM core code. This also enables the test cases to
work more independently from the kernel's configuration.
Patches 9 to 11 split the panic-handling code into the core and panic
helpers. The former maintain all state, locking and public interfaces.
The latter handles drawing and details of the involved framebuffers.
DRM devices that offer panic handling provide a single callback, struct
drm_plane_funcs.display_panic_screen. A new initializer macro makes it
point to the existing panic-drawing implementation. Hence there's no
change in features or functionality. If panic handling is configured
off, it all clears out to NULL.
Patch 12 reworks the test cases slighly, so that they can be build as
a separate module. Do 'modprobe drm_panic_helper_test' to run them.
Tested under bochs with debugfs and test cases.
Overall the series looks good to me, and I like the split between the
helper and the core.
I would just drop the first two patches, as I don't see much difference
between static allocation or kmalloc() at init, and I think that
memset() the buffers to 0 is not useful in this case.
Best regards,
--
Jocelyn
Future directions:
- Panic handling shares some drawing code with format conversion and
clients. There's even more drawing code in vkms. Later series' can
attempt to unify and harmonize all these implementations in a single
draw module.
- The drawing helper drm_plane_helper_display_panic_screen() still
implements various access schemes (map, set_pixel, memcpy) in a single
function. It could be split up into specifialized helpers.
- If we ever need a driver-specific helper, it is now possible to
implement a custom version of display_panic_screen.
Thomas Zimmermann (12):
drm/panic: Allocate QR-code buffers statically
drm/panic: Make allocation of zlib workspace more robust
drm/panic: Return -EINVAL if font is not available
drm/panic: Return errno codes if panic output fails
drm/panic: Pass colors to draw_panic_dispatch()
drm/panic: Pass global module parameters to drm_panic_dispatch()
drm/panic: Retry in dispatch function if panic output fails
drm/panic: Split draw_panic_plane()
drm/panic: Display panic screen via per-plane callback
drm/panic: Internalize panic locking in DRM core and helpers
drm/panic: Move panic display code into helper library
drm/panic: Compile KUnit tests as module
Documentation/gpu/drm-kms-helpers.rst | 11 +-
Documentation/gpu/drm-kms.rst | 3 +
MAINTAINERS | 11 +-
drivers/gpu/drm/Kconfig | 5 +
drivers/gpu/drm/Kconfig.debug | 1 +
drivers/gpu/drm/Makefile | 3 +-
.../amd/display/amdgpu_dm/amdgpu_dm_plane.c | 2 +
drivers/gpu/drm/ast/ast_mode.c | 2 +
drivers/gpu/drm/drm_atomic_helper.c | 2 +-
drivers/gpu/drm/drm_crtc_internal.h | 2 -
drivers/gpu/drm/drm_drv.c | 3 +-
drivers/gpu/drm/drm_kms_helper_common.c | 14 +
drivers/gpu/drm/drm_panic.c | 914 +----------------
drivers/gpu/drm/drm_panic_helper.c | 915 ++++++++++++++++++
...drm_panic_qr.rs => drm_panic_helper_qr.rs} | 4 +-
drivers/gpu/drm/drm_panic_internal.h | 59 ++
drivers/gpu/drm/hyperv/hyperv_drm_modeset.c | 2 +
drivers/gpu/drm/i915/display/i9xx_plane.c | 3 +
.../drm/i915/display/skl_universal_plane.c | 4 +
drivers/gpu/drm/imx/ipuv3/ipuv3-plane.c | 2 +
drivers/gpu/drm/mgag200/mgag200_drv.h | 4 +-
drivers/gpu/drm/nouveau/dispnv50/wndw.c | 2 +
.../gpu/drm/renesas/rcar-du/rcar_du_plane.c | 2 +
.../drm/renesas/shmobile/shmob_drm_plane.c | 2 +
drivers/gpu/drm/sysfb/drm_sysfb_helper.h | 4 +-
drivers/gpu/drm/sysfb/vesadrm.c | 1 +
drivers/gpu/drm/tests/Makefile | 1 +
...m_panic_test.c => drm_panic_helper_test.c} | 65 +-
drivers/gpu/drm/tidss/tidss_plane.c | 2 +
drivers/gpu/drm/tiny/bochs.c | 4 +-
drivers/gpu/drm/virtio/virtgpu_plane.c | 2 +
include/drm/drm_mode_config.h | 4 +-
include/drm/drm_modeset_helper_vtables.h | 11 +-
include/drm/drm_panic.h | 117 +--
include/drm/drm_panic_helper.h | 40 +
include/drm/drm_plane.h | 57 ++
rust/bindings/bindings_helper.h | 4 +-
37 files changed, 1253 insertions(+), 1031 deletions(-)
create mode 100644 drivers/gpu/drm/drm_panic_helper.c
rename drivers/gpu/drm/{drm_panic_qr.rs => drm_panic_helper_qr.rs} (99%)
create mode 100644 drivers/gpu/drm/drm_panic_internal.h
rename drivers/gpu/drm/tests/{drm_panic_test.c => drm_panic_helper_test.c}
(80%)
create mode 100644 include/drm/drm_panic_helper.h
base-commit: dc462ab791b686c48545c160ecc81be64f77a846
prerequisite-patch-id: c67e5d886a47b7d0266d81100837557fda34cb24
prerequisite-patch-id: a5a973e527c88a5b47053d7a72aefe0b550197cb
prerequisite-patch-id: b9adc9622920a3e70168e672c2c92795b3e3a106
prerequisite-patch-id: 5030de433a01c2e99056cadb676a8e2ba35f055a
