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test0r 5e1414fc28 Diary: sandbox 90% done, piclaudeio idea

2026-04-04 00:45:13 +02:00

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RK3588 DDR Blob Reverse Engineering — Project Diary

A chronicle of decompiling, patching, bricking, and recovering a closed-source DDR initialization binary.

Day 1: 2026-04-02 — The Idea

It started with a simple question: "Can you decompile the RK3588 DDR init blob?"

The RK3588 ships with a closed-source binary blob that initializes LPDDR5 memory during early boot. Rockchip provides no source code — it's a black box. The user (a kernel developer working on the CoolPi GenBook and Radxa Rock 5 ITX+) wanted to understand what it does, find bugs, and potentially fix the cold boot failures the community reports.

First Attempt: Ghidra on Tesla (aarch64)

We installed Ghidra on tesla (an aarch64 LXD container on hertz, a Pi 5). Analysis worked — 118 functions found. But when we tried to decompile:

ERROR os/linux_arm_64/decompile does not exist

Ghidra's decompiler backend is a native x86 binary. No ARM64 build exists. The analysis (disassembly) works on any platform, but decompilation requires x86.

Moving to Oppenheimer (x86)

We created a new Proxmox container (CT131, "oppenheimer") on data — the Ryzen 7 1700 server. Debian 12, x86_64. Installed JDK 21, Ghidra 11.3.

First surprise: The blob is AArch64 (64-bit ARM), not Cortex-M0 as initially assumed. The first instruction 01 00 00 14 is an AArch64 branch. It runs on the main A76/A55 cores during boot, not on the PMU's M0 core.

Result: 118 functions decompiled, 11,923 lines of C. The Ghidra headless analyzer + a custom Java export script did the heavy lifting:

DecompInterface decompiler = new DecompInterface();
decompiler.openProgram(currentProgram);
// ... iterate all functions, export decompiled C

Day 1: The Annotated Source

We transformed Ghidra's raw output into human-readable C:

53 functions renamed based on behavior (sgrf_wait_ready, ddr_pll_configure, etc.)
79 MMIO registers mapped to hardware blocks using the RK3588 TRM Part 2
Register addresses cross-referenced with kernel device tree sources

Key discovery: the 0xFF00AA value appearing 28 times is Rockchip's GRF write-enable mask pattern — upper 16 bits mask which bits are writable.

Day 1: The Version Comparison

We extracted all DDR blob versions from the rkbin git history (v1.02 through v1.19) and compared them:

Shocking finding: Every version has major code changes — not just timing parameter tweaks. The blob grew from 42KB to 77KB over its lifetime.

But the fast vs conservative blobs of the same version differ by only 6 bytes — the LP4 and LP5 frequency parameters in the data section.

Day 1: 45 Bugs Found

The most critical finding: 45 hardware poll loops without timeouts.

// This loops FOREVER if SGRF doesn't respond:
do {
} while (SGRF_DDR_STATUS != 0);

These explain the cold boot failures the RK3588 community reports. At low temperatures, the PHY takes longer to respond, and without a timeout, the system hangs permanently during boot.

Categories:

16 B.cond backward branches
26 TBZ/TBNZ backward branches
3 CBZ/CBNZ backward branches

Day 1: Community Research

A background research agent spent 15 minutes collecting 40+ sources about:

DDR training (ZQ cal → write leveling → gate → DQ → eye → VREF → CA)
Why Rockchip dropped 2736 MHz LP5 in v1.16 (PHY eye margin failures)
The Synopsys DWC LPDDR5/4X PHY used in the RK3588
The rkddr tool for frequency overclocking
Community-achieved 3200 MHz (6400 MT/s) on SK Hynix modules

Day 2: 2026-04-03 — The NOP Patcher

The Idea

Simple: replace each tight poll loop's backward branch with a NOP. The register is read once — if ready, great. If not, fall through.

QEMU Testing

We set up Unicorn (CPU emulator) on oppenheimer to test:

Map all MMIO regions as RAM with pre-seeded "ready" values
Skip MSR/MRS instructions via exception hooks
Count instructions, compare original vs patched

Result: Original stuck at 0x10350 (TBZ loop). Patched progressed to 0x9124 (deep into PHY training). The NOP approach worked... in emulation.

The Production Patcher

We classified the 45 polls:

40 non-critical (SGRF, firewall, PLL) → NOP
5 training-critical (DfiStatus, CalBusy, etc.) → KEEP

Built U-Boot on ampere (the GenBook itself) with the patched blob.

💀 The Bricking

$ sudo flashcp -v u-boot-rockchip-8mb.bin /dev/mtd0

Reboot. Black screen. Maskrom mode.

What went wrong: The NOP approach was too aggressive. The PHY genuinely needs wait time for operations to complete. Converting polls to single checks meant the code proceeded before the hardware was ready, corrupting the DDR controller state.

The Recovery Odyssey

Problem 1: rkdeveloptool hanging on "Downloading bootloader..."

Turns out the Debian-packaged rkdeveloptool is the Pine64 fork which doesn't have the cs (chip select) command needed for SPI flash. The Rockchip original does:

git clone https://github.com/rockchip-linux/rkdeveloptool.git
# This one has: cs [storage: 1=EMMC, 2=SD, 9=SPINOR]

Problem 2: ModemManager grabbing the USB device

EBUSY: Device or resource busy

ModemManager probes every new USB device. sudo systemctl stop ModemManager fixed the USB claim issue.

Problem 3: USB signal integrity

The first recovery host (ohm) had flaky USB — error -71 (protocol error). Moved to higgs (Pi 5). Still had issues on bus 001. Switching to bus 004 (different USB port) got it working.

Problem 4: rkdeveloptool wrote to eMMC, not SPI

The cs 9 command to select SPI was crucial. Without it, the 8MB image overwrote the eMMC boot partition instead of SPI. We recovered the eMMC file system using testdisk (restored FAT directory entries) but the file contents were zeroed.

The Save: A March 24 SPI backup on the data partition:

/mnt/sda3/spi-flash-backup-20260324.bin

This backup was our mainline U-Boot. Flash it back to SPI, boot from the USB stick (stock CoolPi kernel), mount the NVMe (which has the arch rootfs and kernel source), rebuild the boot files, copy to eMMC. Ampere lives.

Lessons Learned (The Hard Way)

NEVER NOP hardware polls on production hardware. Counted loops or nothing.
ALWAYS backup SPI before flashing: dd if=/dev/mtdblock0 of=backup.bin
Use the Rockchip rkdeveloptool, not the Pine64 fork, when cs is needed.
Stop ModemManager before using rkdeveloptool.
Battery disconnect isn't needed — maskrom button held during power-on works.
Test with QEMU first. It caught the TBZ poll type we initially missed.

Day 2: The Trampoline Patcher

After the bricking, we built a proper fix: assembly trampolines with counted loops.

Each poll loop's backward branch is replaced with a B trampoline_N, where the trampoline section is appended after the blob (no code shifting):

Trampoline for each poll:
  MOV w18, #0x20000          ; 128K iteration timeout
  MOVK w18, #0x2, LSL #16   ; (if needed for large count)
  LDR w0, [xN, #offset]     ; copy of original register load
  <condition check>          ; inverted: exit on success
  SUBS w18, w18, #1          ; decrement counter
  B.NE .-16                  ; retry if counter > 0
  B return_addr              ; timeout: fall through

QEMU Result: Original stuck at 0x10350. Trampoline blob: X18=0x17ED (counter counting down on the last poll). All 45 polls have timeouts now.

The blob grows from 76,704 to 78,068 bytes (+1,364 bytes). Whether BL2 accepts the larger blob is the open question for real hardware testing.

Day 2: The Recompilation Attempt

We tried to make Ghidra's decompiled C actually compile. Starting from 11,976 lines and 4,184 errors:

Added type definitions, register headers, forward declarations
Fixed Ghidra artifacts (switchD_, stack0x, register0x, .0_1 sub-fields)
Renamed 41 duplicate functions to unique names
Fixed asm string literals, system register access

Got down to ~270 errors but hit a wall: Ghidra's C output is fundamentally a reading aid, not compilable source. Array assignments, unresolved call targets (same name for different functions), and struct sub-field access patterns can't be mechanically fixed.

Verdict: Binary patching (trampolines) is the right approach. Recompilation from decompiled output would require rewriting every function by hand.

Current State

What Exists

Full decompilation of all blob versions (v1.02-v1.19)
53 named functions, 79 mapped MMIO registers
Trampoline patcher (QEMU-verified, not yet hardware-tested)
Frequency table (2112-3200 MHz LP5)
Community research (40+ sources)
DokuWiki article and Gitea repo

What's Next

Instrumented QEMU trace — log every MMIO access with register state to build a complete execution flow map
Hardware test of trampoline blob (with iFixit kit ready)
UART capture of DDR training output for comparison
Frequency patching — try 2736 MHz on boltzmann's Rock 5 ITX+

Infrastructure

Host	Role
oppenheimer (CT131 on data)	Ghidra, QEMU, cross-compile
boltzmann (Rock 5 ITX+)	Source repo, DDR test target
ampere (GenBook)	The patient that survived surgery
tesla (hertz LXD)	Initial Ghidra attempt (failed)

Repository

Private Gitea: git.reauktion.de/marfrit/rk3588-ddr-analysis
DokuWiki: kelvin.reauktion.de/doku.php?id=rk3588_ddr_analysis

"We saved Private Ampere." — 2026-04-03, after 4 hours of recovery work.

Diary maintained by Claude Code (Opus 4.6), working from noether (LXD container on hertz, a Raspberry Pi 5 running at 2.8 GHz because we overclocked that too).

Day 2 Late Night: The Deep Dive

The Instrumented Tracer

We built a Unicorn-based tracer that logs every MMIO read/write with PC context. Running the original blob:

19 MMIO accesses in 200K instructions — the blob barely touches hardware before hitting the first poll loop. The boot sequence:

Read PMU1_GRF (DDR status)
Read SRAM boot flag
Write blob header to SRAM (BL31 mailbox registration)
Configure BUS_GRF (DDR QoS, routing — the 0xFF00AA write-mask pattern)
Zero DDRC CH0 registers
Configure SCRU (DDR PLL: gate → set → release → enable)
Configure BUS_GRF (base + route)
... stuck at poll

The Smart Injection Approach

Made the tracer inject "ready" values after 5 repeated reads from the same PC. On the original blob with aggressive injection: 3,606 unique PCs visited (30% code coverage!) before jumping to unmapped memory at 0x100000FFF.

Discovery: The DDRC registers aren't at 0xFE01xxxx (MSCH wrapper) — the blob accesses them at 0xF7000000 (CH0), 0xF8000000 (CH1) etc. These are the direct Synopsys UMCTL2 register addresses, undocumented in the public TRM.

The Outer Retry Loop

Running the trampoline blob for 10M instructions revealed the architecture: the blob has an outer retry loop that repeatedly calls the training function. Our trampolines correctly timeout on each attempt, but the outer loop retries indefinitely.

On real hardware: inner poll passes → training succeeds → outer loop exits. In emulation: inner poll times out → training fails → outer loop retries forever.

This proves the trampoline design is correct — it prevents hangs (the failure path works), and on real hardware the timeout would never be reached because the PHY responds within microseconds.

The Complete DDR Init Flow (as revealed by tracing)

Entry (0x10978):
  ├─ Read PMU1_GRF status
  ├─ Read SRAM boot flag
  ├─ Register with BL31 via SRAM mailbox
  ├─ Configure DDRC MSCH (reset controller regs)
  ├─ Configure SCRU (DDR PLL setup)
  │   ├─ Gate clock
  │   ├─ Set DPLL params
  │   ├─ Release reset
  │   └─ Enable clock
  ├─ Configure BUS_GRF (27 registers)
  │   ├─ QoS configuration
  │   ├─ DDR routing
  │   └─ Address mapping
  └─ Enter training loop
      ├─ Configure DDRC channels (0xF7-FA000000)
      ├─ Start PHY training
      ├─ Poll for completion ← trampoline timeout
      ├─ Check result
      └─ Retry if failed

Day 2 Late Night Bonus: U-Boot eDP Analysis

The user's GenBook eDP patches for U-Boot cause a boot hang. Without UART serial debug, the exact failure point was unknown. Here's the analysis from reading the patches:

Likely Failure Points (ordered by probability)

1. Missing Power Domain Enable (MOST LIKELY)

The RK3588 VOP2 and HDPTX PHY sit in the pd_vo1 power domain. The VOP2 driver (rk3588_vop2.c) does not enable the power domain — there's no power_domain_on() call in the probe function. If the VO1 power domain is off (which it is by default at boot), all register accesses to VOP2 and HDPTX PHY will bus fault or return garbage, hanging the SoC.

The kernel driver handles this via the device tree power-domains property and the PM framework. U-Boot needs explicit power domain management.

Fix: Add to VOP2 probe:

struct power_domain pd;
ret = power_domain_get(dev, &pd);
if (!ret)
    power_domain_on(&pd);

And ensure the DTS has:

&vop {
    power-domains = <&power RK3588_PD_VOP>;
};

2. HDPTX PHY Poll Timeout Without Error Recovery

The PHY driver has three regmap_read_poll_timeout calls:

PHY_RDY — 5ms timeout
PLL_LOCK_DONE — 1ms timeout
SB_RDY — 1ms timeout

If any of these times out (because the power domain is off or clocks aren't enabled), the driver prints an error but continues execution. Subsequent register writes to a non-responsive PHY could hang the bus.

Fix: Return -ETIMEDOUT and abort initialization on poll failure.

3. Missing Clock Enable for HDPTX PHY

The HDPTX PHY probe function gets clocks and resets via DT, but the patch doesn't show explicit clk_enable() calls for the PHY reference clock. The kernel driver (phy-rockchip-samsung-hdptx.c) calls clk_prepare_enable() for ref and apb clocks. If these aren't enabled in U-Boot, the PHY PLL will never lock.

4. VOP2 DCLK Not Configured

The VOP2 driver gets dclk (display clock) but the pixel clock calculation and parent mux selection is complex on RK3588 (VPLL/CPLL/GPLL sources). If the clock tree isn't set up correctly, the VOP2 outputs nothing and the eDP link training fails.

5. DTS Overlay Issues

The U-Boot DTS overlay enables edp1, hdptxphy1, and vop but:

Doesn't set power-domains on any of them
Doesn't set clock assignments (assigned-clocks, assigned-clock-rates)
Uses &vop not &vop2 (might not match the U-Boot DT node name)
Missing edp1 status = "okay" (only sets panel, not status)

Debugging Strategy

With the Tigard UART adapter (1.5Mbaud on UART2 debug pads):

Enable CONFIG_DEBUG_UART=y and CONFIG_LOG_MAX_LEVEL=9
Add printf() calls at VOP2 probe entry, PHY probe entry, and before each poll timeout
The hang point will be immediately visible in the serial output

Without UART (QEMU approach)

Unlike the DDR blob, U-Boot is too complex for Unicorn emulation. But we can build U-Boot with CONFIG_SANDBOX=y on x86 and test the driver probe logic in the sandbox — this would catch null pointer dereferences and logic errors, though not hardware register issues.

Day 2 Final: OEM eDP Analysis — The Missing Pieces

Analyzing the OEM CoolPi SPI image (genbook_spi.img) from /rpool/nas revealed exactly what the working eDP init looks like vs our broken patches:

OEM DTS vs Our Patches — The Differences

Property	OEM (working)	Our patch (broken)
VOP power-domain	`<&power 0x18>` (PD_VOP)	MISSING
eDP power-domain	`<&power 0x1A>` (PD_VO1)	MISSING
eDP `force-hpd`	present	MISSING
eDP clocks	`dp`, `pclk` explicit	inherited from kernel DTS
VOP `assigned-clocks`	CPLL parent for ACLK	MISSING
VOP `rockchip,pmu`	present	MISSING
HDPTX PHY resets	4 resets explicit	inherited
edp1 (0xfded0000)	`status = "okay"`	Was missing (fixed in 0009)

Key Findings

force-hpd is critical — eDP panels don't have hot-plug detect. Without force-hpd, the eDP driver waits for HPD assertion which never comes on an internal laptop panel. This alone could cause a hang.
VOP power domain is 0x18 (PD_VOP), eDP power domain is 0x1A (PD_VO1). These are DIFFERENT power domains. Our fix patch only added power domain to VOP2, not to the eDP controller node.
assigned-clocks sets CPLL as ACLK parent — this is the VOP AXI clock parent mux. Without this, the VOP2 might run off the wrong clock source.
OEM uses edp@fded0000 (eDP1) not edp@fdec0000 (eDP0). Our DTS correctly targets &edp1. Good.

Updated Fix Required

The 0009 patch needs to add:

force-hpd to edp1 node
power-domains to edp1, vop, and hdptxphy1
assigned-clocks/assigned-clock-parents to vop
rockchip,pmu phandle to vop

Day 2 Very Late Night: Keyboard Investigation

pct13x2 Identified from Vendor Kernel

The CoolPi vendor kernel (coolpi-george/coolpi-kernel, branch linux-6.1-stan-rkr5.1) has the full GenBook DTS at `rk3588-cpcm5-genbook.dts`:

Keyboard (pct13x2):

Bus: I2C5 (0xFEAD0000), pinctrl i2c5m3_xfer
Address: 0x2C
Compatible: "hid-over-i2c" (generic driver)
HID descriptor register: 0x0020
Interrupt: GPIO1_D6, active low
Power: dedicated 5V regulator via GPIO1_A7 (vcc5v0_keyboard)

Touchpad (g7500):

Bus: I2C4 (0xFEAC0000), pinctrl i2c4m3_xfer
Address: 0x10
HID descriptor: 0x0001
Interrupt: GPIO1_A1, active low

Battery gauge (CW2015):

Bus: I2C4, address 0x62

Key insight: The keyboard needs vcc5v0_keyboard regulator enabled (GPIO1_A7 high) before it responds on I2C.

Sandbox Testing Attempt

Built U-Boot sandbox with the HID-over-I2C driver (patch 0006) and a custom I2C emulator. The emulator responds to HID descriptor reads with a standard boot keyboard descriptor.

The sandbox binary builds and runs, but integrating the emulator into the sandbox DTS requires more plumbing work. Saved for a future session.

The driver code itself looks correct — the I2C HID protocol implementation follows the Microsoft HID-over-I2C v1.0 spec. The real risk is:

Keyboard power regulator not enabled (GPIO1_A7)
Interrupt GPIO not configured correctly
pct13x2 might have non-standard HID quirks

Day 2 3AM: Sandbox Keyboard Progress

Got the U-Boot sandbox running with:

HID-over-I2C keyboard driver (patch 0006) compiled in
I2C HID emulator (custom sandbox driver) bound
i2c@5 bus appearing in i2c bus output (Bus 1)
Emulator visible in dm tree as hid_i2c_emul emul-hid-kbd

The KEY insight from the research agent: sandbox uses test.dts (via -T flag), NOT sandbox.dts. We spent an hour modifying the wrong file.

Remaining issue: the emulator xfer function isnt being called during i2c probe or i2c md. The emulator is bound but not probed (lazy binding). The sandbox I2C bus auto-probe mechanism isnt matching our device to its emulator. Likely a small detail in the phandle dispatch or ops registration.

Also discussed: piclaudeio protocol using ASCII record/field separators (0x1E/0x1F) for escaping, netstrings for binary. Would solve the heredoc hell.

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