rpi5_mailbox.c: wire the VideoCore mailbox message protocol (FABRIC-3.md §IV.3 item 3)

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New rpi5_mailbox_get_framebuffer() sends one property-tag request buffer
(phys size, virt size, depth, pixel order, virtual offset, allocate-buffer,
get-pitch) over the register layout rpi5_dtb.c already discovers, populating
an Rpi5FramebufferInfo kept in exact field-for-field sync with uefi.h's
FramebufferInfo so console.c/vt100.c/framebuffer.c need no downstream changes
once this is wired into a real entry stub.

Register offsets (+0x00/+0x18 MBOX0 read/status, +0x20/+0x38 MBOX1
write/status) confirmed against a Pi-5-specific bare-metal reference,
independently cross-checked against this codebase's own rpi5_dtb.c
translated base address.

Caught and fixed a real buffer-overflow bug before compiling: the static
request buffer was sized 32 words against an actual 35-word requirement for
the 7-tag sequence, recomputed exactly rather than re-estimated; resized to
40 words.

Two things flagged as genuinely unverified against real hardware (not
guessed past the comment): the allocate-buffer tag's request-size field
value, and whether its response address needs classic bus-alias masking on
Pi 5 specifically.

Compile-only-verified -- no caller yet (that's the still-open entry-stub/DTB
constructor items). Verified 3-arch boot to ok>/zuse)ok>.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019YcT3H2PQeyujrzjqS3Var

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This commit is contained in:

Robert Allan James

2026-09-04 14:00:32 -04:00

co-authored by Claude Sonnet 5

parent ca52ce8243

commit a32b0ebcbe

11 changed files with 27904 additions and 6 deletions

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experiments/bare_metal/runs/doe-aarch64-20260904-135352.csv

experiments/bare_metal/runs/doe-amd64-20260904-134228.csv

experiments/bare_metal/runs/doe-riscv64-20260904-135839.csv