Date:   Mon, 13 Dec 2021 08:58:20 +0530
From:   Sai Prakash Ranjan <quic_saipraka@...cinc.com>
To:     Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Marc Zyngier <maz@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        Steven Rostedt <rostedt@...dmis.org>
CC:     gregkh <gregkh@...uxfoundation.org>, <quic_psodagud@...cinc.com>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-arm-msm@...r.kernel.org>
Subject: Re: [PATCHv6 0/5] tracing/rwmmio/arm64: Add support to trace register
 reads/writes

Hi Arnd,

On 12/7/2021 12:24 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 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):
>    tracing: 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          |  81 +++++++++++++++++++--
>   include/trace/events/rwmmio.h     | 112 ++++++++++++++++++++++++++++++
>   kernel/trace/Kconfig              |   7 ++
>   kernel/trace/Makefile             |   1 +
>   kernel/trace/trace_readwrite.c    |  47 +++++++++++++
>   11 files changed, 278 insertions(+), 54 deletions(-)
>   create mode 100644 include/trace/events/rwmmio.h
>   create mode 100644 kernel/trace/trace_readwrite.c
>

Does this version look good to you? From the other mail thread it seems 
Catalin
is ok with your suggested change. Kernel test robot hasn't come with any 
build error
reports so far, I have fixed the previous reported one in meson drm driver.

Thanks,
Sai

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