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Porting drm-515-kmod to MidnightBSD — Gap Analysis & Plan

Goal

Make graphics/drm-515-kmod (FreeBSD's backport of the Linux 5.15 DRM stack: drm.ko, i915kms, amdgpu, radeonkms, ttm) compile and link against MidnightBSD master. The port officially requires FreeBSD 14.x.

Committed scope: build + link only. Do not kldload. Runtime bring-up (vt/newcons KMS console handoff, interrupts, suspend/resume, modesetting) is out of scope.

Current state

Tree Version LinuxKPI level
MidnightBSD master (/usr/src) __MidnightBSD_version 401002, __FreeBSD_version 1305500 ad-hoc fork, ~FreeBSD 13.5-STABLE + selective forward-ports
FreeBSD 14-STABLE (/home/laffer1/git/freebsd, stable/14) __FreeBSD_version 1404501 reference target

MidnightBSD's sys/compat/linuxkpi is a series of ad-hoc partial imports from FreeBSD 12 → 13 → 13.5, already partly forward-ported (e.g. pci_domain_nr).

Key findings

  1. dma-buf.h / dma-fence.h / dma-resv.h are NOT base gaps. They are absent from both MidnightBSD and FreeBSD 14 base LinuxKPI — the drm-kmod port ships them itself (bundled GPLv2 headers). Not our problem to add.

  2. A wholesale FreeBSD 14 LinuxKPI import is the WRONG approach. Empirically verified: overlaying FreeBSD 14's common/{include,src} and building fails on base-kernel API deltas that recur in nearly every file —

    • sched.h → td_ast_pending / TDA_SCHED (FreeBSD 14 AST framework)
    • net.h → pr_peeraddr / pr_sockaddr (FreeBSD 14 protosw refactor)
    • file.h / linux_compat.c → fget_unlocked, fo_stat_t, const fileops
    • rbtree.h (sys/tree.h macro arity), kmem_free(void*), qsort_r MidnightBSD's base has none of these. Wholesale import would require backporting the AST framework, the protosw refactor, and the file/fileops API into MidnightBSD's base kernel — a larger, riskier project than the drm port itself, destabilizing unrelated subsystems.

  3. MidnightBSD's existing LinuxKPI already correctly targets its 13.5 base. The real gap is the additive FreeBSD 14 files (new headers + new modules), not re-importing existing files.

Approach: hybrid (additive import + targeted backports)

Keep MidnightBSD's existing, base-compatible LinuxKPI files. Add only the genuinely-new FreeBSD 14 pieces drm needs, and backport individual new symbols into existing headers only where they don't drag base-incompatible changes.

Workstream A — LinuxKPI uplift (in /usr/src) — IN PROGRESS

  • Import additive FreeBSD 14 headers (aperture.h, iosys-map.h, hdmi.h, iommu.h, irqdomain.h, ioport.h, io-64-nonatomic-lo-hi.h, cleanup.h, container_of.h, build_bug.h, minmax.h, math.h, limits.h, kstrtox.h, string_helpers.h, nodemask.h, of.h, agp_backend.h, apple-gmux.h, device/, video/, dummy sysfb.h).
  • Add linuxkpi_hdmi and linuxkpi_video modules (HDMI infoframe, ACPI-video/backlight, framebuffer aperture) + register in sys/modules/Makefile. Both build clean.
  • Backport devm_add_action()/devm_add_action_or_reset() (needed by linux_aperture.c).
  • Backport further individual symbols as the drm port build demands them (iterative, localized — keep MidnightBSD base semantics, do NOT pull the AST/protosw/file base reworks).
  • Note: linux_kobject.c is intentionally NOT imported — FreeBSD 14 split it out of linux_compat.c, which MidnightBSD still carries inline (would dup).

Workstream B — Create drm-515-kmod in mports (in /usr/mports) — TODO

NOTE: /usr/ports here is the upstream FreeBSD ports tree and is not operational under MidnightBSD make (bsd.port.options.mk not found, ${OPSYS} conditionals malformed). MidnightBSD uses mports at /usr/mports, which already ships a MidnightBSD-adapted graphics/drm-510-kmod (uses bsd.mport.options.mk, IGNORE_MidnightBSD_3.x, already CONFLICTS_INSTALL with drm-515-kmod) and gpu-firmware-kmod.

  • Create graphics/drm-515-kmod by copying mports drm-510-kmod and bumping Makefile.version to 5.15.160 / drm_v5.15.160_6; refresh distinfo, pkg-plist, and the extra-patch-linuxkpi-pci (gate decided by build).
  • Build via mports against /usr/src (our uplifted LinuxKPI); iterate base-compat backports (Workstream A) as drm source demands them.
  • mports is a separate git repo (MidnightBSD/mports) → a second PR.

Verification (build-only; do NOT kldload)

  1. cd /usr/src/sys/modules/linuxkpi{,_hdmi,_video} && make — clean. (done)
  2. cd /usr/ports/graphics/drm-515-kmod && make — no IGNORE; produces drm/i915kms/amdgpu/radeonkms/ttm .ko.
  3. nm -u the .kos for unresolved LinuxKPI symbols against the built kernel.
  4. cppcheck/clang-format sanity on any base-compat backport commits.

Out of scope (follow-on)

kldload, vt/newcons KMS console handoff, interrupts, suspend/resume, on-hardware modesetting.

Result — DONE (build + link verified)

All six modules build and link clean against MidnightBSD (__FreeBSD_version 1305500) on amd64, via cd /usr/mports/graphics/drm-515-kmod && make build SRC_BASE=/usr/src:

dmabuf.ko  drm.ko  ttm.ko  amdgpu.ko  i915kms.ko  radeonkms.ko

(All valid ELF 64-bit LSB relocatable kmods. Not loaded — out of scope.)

LinuxKPI changes (src branch feature/drm-515-kmod-linuxkpi)

Additive FreeBSD 14 import (headers + linuxkpi_hdmi/linuxkpi_video modules) plus targeted backports, each driven by a real build failure:

  • single-arg vm_operations_struct.fault; kernel.h→math64.h
  • devm_add_action()/_or_reset(); pcie_aspm_enabled(); INTEL_FAM6 Alder Lake
  • noinline_for_stack; bitmap_to_arr32(); acpi_put_table()
  • move BUILD_BUG → build_bug.h; move U*_MAX → limits.h (both included from kernel.h)
  • self-contained dmi.h errno; import util_macros.h, time64.h
  • tasklet callback API (tasklet_setup, from_tasklet, ->callback) + ZERO_SIZE_PTR
  • PCI/device power bits (dev_pm_info, pci_dev.current_state, pci_power_name(), pci_power_names[])

Existing LinuxKPI files were intentionally NOT re-imported wholesale (would require backporting the FreeBSD 14 AST/protosw/file base reworks).

Port (mports branch feature/drm-515-kmod)

graphics/drm-515-kmod from drm-510-kmod; two source patches for FreeBSD-14 assumptions vs MidnightBSD base (dma_buf_stat thread arg; i915 totalram_pages gated on __MidnightBSD_version).

Not done (follow-on)

kldload and runtime bring-up (vt/newcons KMS handoff, IRQs, suspend/resume, modesetting); powerpc64 acpi_iicbus guard; gpu-firmware-kmod packaging.