Date:   Sat,  3 Jun 2017 22:42:52 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     Mathieu Poirier <mathieu.poirier@...aro.org>,
        Will Deacon <will.deacon@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Mike Leach <mike.leach@...aro.org>,
        Chunyan Zhang <zhang.chunyan@...aro.org>
Cc:     Leo Yan <leo.yan@...aro.org>
Subject: [PATCH v1 0/4] coresight: support panic dump functionality

### Introduction ###

Embedded Trace Buffer (ETB) provides on-chip storage of trace data,
usually has buffer size from 2KB to 8KB. These data has been used for
profiling and this has been well implemented in coresight driver.

This patch set is to explore ETB RAM data for postmortem debugging.
We could consider ETB RAM data is quite useful for postmortem debugging,
especially if the hardware design with local ETB buffer (ARM DDI 0461B)
chapter 1.2.7. 'Local ETF', with this kind design every CPU has one
dedicated ETB RAM. So it's quite handy that we can use alive CPU to help
dump the hang CPU ETB RAM. Then we can quickly get to know what's the
exact execution flow before its hang.

Due ETB RAM buffer has small size, if all CPUs shared one ETB buffer
then the trace data for causing error is easily to be overwritten by
other PEs; but even so sometimes we still have chance to go through the
trace data to assist debugging panic issues.

### Implementation ###

Firstly we need provide a unified APIs for panic dump functionality, so
it can be easily extended to enable panic dump for multiple drivers. This
is finished by patch 0001, it registers panic notifier, and provide the
general APIs {coresight_add_panic_cb|coresight_del_panic_cb} as helper
functions so any coresight device can add into dump list or delete itself
as needed.

Generally all the panic dump specific stuff are related to the sinks
devices, so this initial version code it only supports sink devices; and
Patch 0002 is to add and remove panic callback for sink devices.

Patch 0003 and 0004 are to add panic callback functions for tmc and etb10
drivers; so these two drivers can save specific trace data when panic
happens.

NOTE: patch 0003 for tmc driver panic callback which has been verified on
Hikey board. patch 0004 for etb10 has not been tested due lack hardware
in hand.

### Usage ###

Below are the example for how to use panic dump functionality on 96boards
Hikey, the brief flow is: when the panic happens the ETB panic callback
function saves trace data into memory, then relies on kdump to use
recovery kernel to save DDR content as kernel core dump file; after we
transfer kernel core dump file from board to host PC, use 'crash' tool to
extract the coresight ETB trace data; finally we can use python script
to generate perf format compatible file and use 'perf' to output the
readable execution flow.

- Save trace data into memory with kdump on Hikey:

  ARM64's kdump supports to use the same kernel image both for main
  kernel and dump-capture kernel; so we can simply to load dump-capture
  kernel with below command:
  ./kexec -p vmlinux --dtb=hi6220-hikey.dtb --append="root=/dev/mmcblk0p9
  rw  maxcpus=1 reset_devices earlycon=pl011,0xf7113000 nohlt
  initcall_debug console=tty0 console=ttyAMA3,115200 clk_ignore_unused"

  Enable the coresight path for ETB device:
  echo 1 > /sys/bus/coresight/devices/f6402000.etf/enable_sink
  echo 1 > /sys/bus/coresight/devices/f659c000.etm/enable_source
  echo 1 > /sys/bus/coresight/devices/f659d000.etm/enable_source
  echo 1 > /sys/bus/coresight/devices/f659e000.etm/enable_source
  echo 1 > /sys/bus/coresight/devices/f659f000.etm/enable_source
  echo 1 > /sys/bus/coresight/devices/f65dc000.etm/enable_source
  echo 1 > /sys/bus/coresight/devices/f65dd000.etm/enable_source
  echo 1 > /sys/bus/coresight/devices/f65de000.etm/enable_source
  echo 1 > /sys/bus/coresight/devices/f65df000.etm/enable_source

- After kernel panic happens, the kdump launches dump-capture kernel;
  so we need save kernel's dump file on target:
  cp /proc/vmcore ./vmcore

  After we download vmcore file from Hikey board to host PC, we can
  use 'crash' tool to check coresight dump info and extract trace data:
  crash vmlinux vmcore
  crash> log
  [   37.559337] coresight f6402000.etf: invoke panic dump...
  [   37.565460] coresight-tmc f6402000.etf: Dump ETB buffer 0x2000@...fff80003b8da180
  crash> rd 0xffff80003b8da180 0x2000 -r cs_etb_trace.bin

- Use python script perf_cs_dump_wrapper.py to wrap trace data for
  perf format compatible file and finally use perf to output CPU
  execution flow:

  On host PC run python script, please note now this script is not flexbile
  to support all kinds of coresight topologies, this script still has hard coded
  info related with coresight specific topology in Hikey:
  python perf_cs_dump_wrapper.py -i cs_etb_trace.bin -o perf.data

  On Hikey board:
  ./perf script -v -F cpu,event,ip,sym,symoff --kallsyms ksymbol -i perf.data -k vmlinux

  [002]          instructions:  ffff0000087d1d60 psci_cpu_suspend_enter+0x48
  [002]          instructions:  ffff000008093400 cpu_suspend+0x0
  [002]          instructions:  ffff000008093210 __cpu_suspend_enter+0x0
  [002]          instructions:  ffff000008099970 cpu_do_suspend+0x0
  [002]          instructions:  ffff000008093294 __cpu_suspend_enter+0x84
  [002]          instructions:  ffff000008093428 cpu_suspend+0x28
  [002]          instructions:  ffff00000809342c cpu_suspend+0x2c
  [002]          instructions:  ffff0000087d1968 psci_suspend_finisher+0x0
  [002]          instructions:  ffff0000087d1768 psci_cpu_suspend+0x0
  [002]          instructions:  ffff0000087d19f0 __invoke_psci_fn_smc+0x0

Have uploaded related tools into folder:
http://people.linaro.org/~leo.yan/debug/coresight_dump/

Changes from RFC:
* Follow Mathieu's suggestion, use general framework to support dump
  functionality.
* Changed to use perf to analyse trace data.

Leo Yan (4):
  coresight: support panic dump functionality
  coresight: add and remove panic callback for sink
  coresight: tmc: hook panic callback for ETB/ETF
  coresight: etb10: hook panic callback

 drivers/hwtracing/coresight/Kconfig                |  10 ++
 drivers/hwtracing/coresight/Makefile               |   1 +
 drivers/hwtracing/coresight/coresight-etb10.c      |  16 +++
 drivers/hwtracing/coresight/coresight-panic-dump.c | 130 +++++++++++++++++++++
 drivers/hwtracing/coresight/coresight-priv.h       |  10 ++
 drivers/hwtracing/coresight/coresight-tmc-etf.c    |  26 +++++
 drivers/hwtracing/coresight/coresight.c            |  11 ++
 include/linux/coresight.h                          |   2 +
 8 files changed, 206 insertions(+)
 create mode 100644 drivers/hwtracing/coresight/coresight-panic-dump.c

-- 
2.7.4

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