[PATCHv9 0/5] lib/rwmmio/arm64: Add support to trace register reads/writes

Sai Prakash Ranjan quic_saipraka at quicinc.com
Tue Feb 8 01:31:10 PST 2022


On 2/1/2022 12:26 AM, Sai Prakash Ranjan wrote:
> Hi Arnd, Steve
>
> On 1/24/2022 12:03 PM, Sai Prakash Ranjan wrote:
>> Generic MMIO read/write i.e., __raw_{read,write}{b,l,w,q} accessors
>> are typically used to read/write from/to memory mapped registers
>> and can cause hangs or some undefined behaviour in following cases,
>>
>> * If the access to the register space is unclocked, for example: if
>>    there is an access to multimedia(MM) block registers without MM
>>    clocks.
>>
>> * If the register space is protected and not set to be accessible from
>>    non-secure world, for example: only EL3 (EL: Exception level) access
>>    is allowed and any EL2/EL1 access is forbidden.
>>
>> * If xPU(memory/register protection units) is controlling access to
>>    certain memory/register space for specific clients.
>>
>> and more...
>>
>> Such cases usually results in instant reboot/SErrors/NOC or interconnect
>> hangs and tracing these register accesses can be very helpful to debug
>> such issues during initial development stages and also in later stages.
>>
>> So use ftrace trace events to log such MMIO register accesses which
>> provides rich feature set such as early enablement of trace events,
>> filtering capability, dumping ftrace logs on console and many more.
>>
>> Sample output:
>>
>> rwmmio_write: __qcom_geni_serial_console_write+0x160/0x1e0 width=32 
>> val=0xa0d5d addr=0xfffffbfffdbff700
>> rwmmio_post_write: __qcom_geni_serial_console_write+0x160/0x1e0 
>> width=32 val=0xa0d5d addr=0xfffffbfffdbff700
>> rwmmio_read: qcom_geni_serial_poll_bit+0x94/0x138 width=32 
>> addr=0xfffffbfffdbff610
>> rwmmio_post_read: qcom_geni_serial_poll_bit+0x94/0x138 width=32 
>> val=0x0 addr=0xfffffbfffdbff610
>>
>> This series is a follow-up for the series [1] and a recent series [2] 
>> making use
>> of both.
>>
>> [1] 
>> https://lore.kernel.org/lkml/cover.1536430404.git.saiprakash.ranjan@codeaurora.org/
>> [2] 
>> https://lore.kernel.org/lkml/1604631386-178312-1-git-send-email-psodagud@codeaurora.org/
>>
>> Note in previous v4 version, Arnd suggested to benchmark and compare 
>> size with callback
>> based implementation, please see [3] for more details on that with 
>> brief comparison below.
>>
>>
>> **Inline version with CONFIG_FTRACE=y and CONFIG_TRACE_MMIO_ACCESS=y**
>> $ size vmlinux
>>     text           data             bss     dec hex         filename
>>   23884219        14284468         532568 38701255 24e88c7        
>> vmlinux
>>
>> **Callback version with CONFIG_FTRACE=y and CONFIG_TRACE_MMIO_ACCESS=y**
>> $ size vmlinux
>>      text          data             bss     dec hex        filename
>>   24108179        14279596         532568 38920343 251e097       vmlinux
>>
>> $ ./scripts/bloat-o-meter inline-vmlinux callback-vmlinux
>> add/remove: 8/3 grow/shrink: 4889/89 up/down: 242244/-11564 (230680)
>> Total: Before=25812612, After=26043292, chg +0.89%
>>
>> [3] 
>> https://lore.kernel.org/lkml/466449a1-36da-aaa9-7e4f-477f36b52c9e@quicinc.com/
>>
>> Changes in v9:
>>   * Use TRACE_EVENT_CLASS for rwmmio_write and post_write (Steven 
>> Rostedt)
>>
>> Changes in v8:
>>   * Fix build error reported by kernel test robot.
>>
>> Changes in v7:
>>   * Use lib/ instead of kernel/trace/ based on review comment by 
>> Steven Rostedt.
>>
>> Changes in v6:
>>   * Implemented suggestions by Arnd Bergmann:
>>     - Use arch independent IO barriers in arm64/asm
>>     - Add ARCH_HAVE_TRACE_MMIO_ACCESS
>>     - Add post read and post write logging support
>>     - Remove tracepoint_active check
>>   * Fix build error reported by kernel test robot.
>>
>> Changes in v5:
>>   * Move arm64 to use asm-generic provided high level MMIO accessors 
>> (Arnd).
>>   * Add inline logging for MMIO relaxed and non-relaxed accessors.
>>   * Move nVHE KVM comment to makefile (Marc).
>>   * Fix overflow warning due to switch to inline accessors instead of 
>> macro.
>>   * Modify trace event field to include caller and parent details for 
>> more detailed logs.
>>
>> Changes in v4:
>>   * Drop dynamic debug based filter support since that will be 
>> developed later with
>>     the help from Steven (Ftrace maintainer).
>>   * Drop value passed to writel as it is causing hangs when tracing 
>> is enabled.
>>   * Code cleanup for trace event as suggested by Steven for earlier 
>> version.
>>   * Fixed some build errors reported by 0-day bot.
>>
>> Changes in v3:
>>   * Create a generic mmio header for instrumented version (Earlier 
>> suggested in [1]
>>     by Will Deacon and recently [2] by Greg to have a generic version 
>> first).
>>   * Add dynamic debug support to filter out traces which can be very 
>> useful for targeted
>>     debugging specific to subsystems or drivers.
>>   * Few modifications to the rwmmio trace event fields to include the 
>> mmio width and print
>>     addresses in hex.
>>   * Rewrote commit msg to explain some more about usecases.
>>
>> Prasad Sodagudi (1):
>>    lib: Add register read/write tracing support
>>
>> Sai Prakash Ranjan (4):
>>    arm64: io: Use asm-generic high level MMIO accessors
>>    irqchip/tegra: Fix overflow implicit truncation warnings
>>    drm/meson: Fix overflow implicit truncation warnings
>>    asm-generic/io: Add logging support for MMIO accessors
>>
>>   arch/Kconfig                      |  3 +
>>   arch/arm64/Kconfig                |  1 +
>>   arch/arm64/include/asm/io.h       | 41 +++----------
>>   arch/arm64/kvm/hyp/nvhe/Makefile  |  7 ++-
>>   drivers/gpu/drm/meson/meson_viu.c | 22 +++----
>>   drivers/irqchip/irq-tegra.c       | 10 ++--
>>   include/asm-generic/io.h          | 82 ++++++++++++++++++++++++--
>>   include/trace/events/rwmmio.h     | 97 +++++++++++++++++++++++++++++++
>>   lib/Kconfig                       |  7 +++
>>   lib/Makefile                      |  2 +
>>   lib/trace_readwrite.c             | 47 +++++++++++++++
>>   11 files changed, 265 insertions(+), 54 deletions(-)
>>   create mode 100644 include/trace/events/rwmmio.h
>>   create mode 100644 lib/trace_readwrite.c
>>
>>
>> base-commit: bd8d9cef2a7932e688ca267ea1adf5ea6557c777
>
> Any comments on this version?
>
> Thanks,
> Sai

Gentle Ping!

Thanks,
Sai



More information about the linux-arm-kernel mailing list