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[Qemu-devel] [Bug 1826827] Re: dtc crash; pnv_dt_serial cannot find lpc'

From: David Gibson
Subject: [Qemu-devel] [Bug 1826827] Re: dtc crash; pnv_dt_serial cannot find lpc's phandle
Date: Thu, 04 Jul 2019 03:25:53 -0000

This assertion should be fixed by upstream commit 8f695676227 "Avoid
assertion in check_interrupts_property()".  That should be included in
dtc v1.5.1 which I hope to release soon.

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  dtc crash; pnv_dt_serial cannot find lpc's phandle

Status in QEMU:

Bug description:
  Qemu version:
  QEMU emulator version 4.0.50 (v4.0.0-142-ge0fb2c3d89)
  Copyright (c) 2003-2019 Fabrice Bellard and the QEMU Project developers

  dtc version:
  Version: DTC 1.5.0-g5c3513f6

  pnv_dt_serial has a line which is supposed to set the interrupt-parent of the 
"isa-serial@i3f8" node to the phandle of "lpc@0".

  To that end, it calls fdt_get_phandle as shown below:
  _FDT((fdt_setprop_cell(fdt, node, "interrupt-parent", fdt_get_phandle(fdt, 

  The function fdt_get_phandle fails to find the property "phandle" (or
  "linux,phandle") for the lpc node. Consequently, pnv_dt_serial sets
  the interrupt-parent to 0.

  Now boot the qemu-system-ppc64 powernv machine, and extract the fdt by
  using the qemu monitor's pmemsave command, taking help of the OPAL
  firmware's messages to locate the fdt in the physical ram.

  qemu-system-ppc64 -m 1g -machine powernv,num-chips=1 \
  -cpu power9 -smp 2,cores=2,threads=1 -accel tcg,thread=multi \
  -kernel ./vmlinux \
  -append 'disable_radix' \
  -serial mon:stdio -nographic -nodefaults

  The kernel vmlinux contains nothing but a single instruction which
  loops infintely, so that we can gather OPAL's messages, especially the
  one below:

  [    0.168845963,5] INIT: Starting kernel at 0x20000000, fdt at
  0x304b0b70 14404 bytes

  Once the fdt is dumped to a file, run the following:

  'dtc -O dtb -I dts -o out.dts dtb'

  After a few warnings, the dtc application crashes because an assertion
  was fired.

  out.dts: Warning (unit_address_vs_reg): /lpcm-opb@6030000000000/lpc@0: node 
has a unit name, but no reg property
  out.dts: Warning (simple_bus_reg): /lpcm-opb@6030000000000/lpc@0: missing or 
empty reg/ranges property
  out.dts: Warning (avoid_unnecessary_addr_size): /ibm,opal: unnecessary 
#address-cells/#size-cells without "ranges" or child "reg" property
  out.dts: Warning (unique_unit_address): /interrupt-controller@0: duplicate 
unit-address (also used in node /memory@0)
  out.dts: Warning (chosen_node_stdout_path): /chosen:linux,stdout-path: Use 
'stdout-path' instead
  dtc: livetree.c:575: get_node_by_phandle: Assertion `generate_fixups' failed.
  Aborted (core dumped)

  The assertion is fired because get_node_by_phandle receives a phandle
  value of 0, which is unexpected, unless fixups are needed (They are
  not, when running the dtc command).

  Back inside pnv_dt_serial, if the line that sets "interrupt-parent"
  for the serial device node is commented out, the dtc crash is
  prevented. Looking at hw/ppc/e500.c, it takes care of allocating
  necessary phandle values in the nodes, so a similar method can be
  adopted for powernv.

  The dtb is attached.

  Edit: Add version, Correct filenames.

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