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From:   Sai Prakash Ranjan <quic_saipraka@quicinc.com>
To:     <arnd@arndb.de>
CC:     <quic_saipraka@quicinc.com>, <catalin.marinas@arm.com>,
        <gregkh@linuxfoundation.org>,
        <linux-arm-kernel@lists.infradead.org>,
        <linux-arm-msm@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        <maz@kernel.org>, <quic_psodagud@quicinc.com>,
        <quic_tsoni@quicinc.com>, <rostedt@goodmis.org>, <will@kernel.org>
Subject: Re: [PATCHv10 0/6] lib/rwmmio/arm64: Add support to trace register reads/writes
Date:   Fri, 8 Apr 2022 16:47:07 +0530
Message-ID: <20220408111707.2488-1-quic_saipraka@quicinc.com>
In-Reply-To: <cover.1644824638.git.quic_saipraka@quicinc.com>
References: <cover.1644824638.git.quic_saipraka@quicinc.com>
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Hi Arnd,

On 2/24/2022 11:37 AM, 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 v10:
>  * Use GENMASK(31, 0) for -Woverflow warning in irqchip tegra driver (Marc).
>  * Convert ETM4x ARM64 driver to use asm-generic IO memory barriers (Catalin).
>  * Collect ack from Catalin for arm64 change.
>
> 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 (5):
>   arm64: io: Use asm-generic high level MMIO accessors
>   coresight: etm4x: Use asm-generic IO memory barriers
>   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 ++---
>  .../coresight/coresight-etm4x-core.c          |  8 +-
>  drivers/hwtracing/coresight/coresight-etm4x.h |  8 +-
>  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 +++++++++
>  13 files changed, 273 insertions(+), 62 deletions(-)
>  create mode 100644 include/trace/events/rwmmio.h
>  create mode 100644 lib/trace_readwrite.c
>
>
> base-commit: 754e0b0e35608ed5206d6a67a791563c631cec07

Gentle ping, could you please take a look at this, would appreciate your reviews.

Thanks,
Sai