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    Subject[PATCH V8 0/7] Add driver support for Data Capture and Compare Engine(DCC) for SM8150,SC7280,SC7180,SDM845
    Date
    DCC(Data Capture and Compare) is a DMA engine designed for debugging purposes.
    In case of a system crash or manual software triggers by the user the DCC hardware
    stores the value at the register addresses which can be used for debugging purposes.
    The DCC driver provides the user with debugfs interface to configure the register
    addresses. The options that the DCC hardware provides include reading from registers,
    writing to registers, first reading and then writing to registers and looping
    through the values of the same register.

    In certain cases a register write needs to be executed for accessing the rest of the
    registers, also the user might want to record the changing values of a register with
    time for which he has the option to use the loop feature.

    The options mentioned above are exposed to the user by debugfs files once the driver
    is probed. The details and usage of this debugfs files are documented in
    Documentation/ABI/testing/debugfs-driver-dcc.

    As an example let us consider a couple of debug scenarios where DCC has been proved to be
    effective for debugging purposes:-

    i)TimeStamp Related Issue

    On SC7180, there was a coresight timestamp issue where it would occasionally be all 0
    instead of proper timestamp values.

    Proper timestamp:
    Idx:3373; ID:10; I_TIMESTAMP : Timestamp.; Updated val = 0x13004d8f5b7aa; CC=0x9e

    Zero timestamp:
    Idx:3387; ID:10; I_TIMESTAMP : Timestamp.; Updated val = 0x0; CC=0xa2

    Now this is a non-fatal issue and doesn't need a system reset, but still needs
    to be rootcaused and fixed for those who do care about coresight etm traces.
    Since this is a timestamp issue, we would be looking for any timestamp related
    clocks and such.

    We get all the clk register details from IP documentation and configure it
    via DCC config_read debugfs node. Before that we set the current linked list.

    /* Program the linked list with the addresses */
    echo R 0x10c004 > /sys/kernel/debug/dcc/../3/config
    echo R 0x10c008 > /sys/kernel/debug/dcc/../3/config
    echo R 0x10c00c > /sys/kernel/debug/dcc/../3/config
    echo R 0x10c010 > /sys/kernel/debug/dcc/../3/config
    ..... and so on for other timestamp related clk registers

    /* Other way of specifying is in "addr len" pair, in below case it
    specifies to capture 4 words starting 0x10C004 */

    echo R 0x10C004 4 > /sys/kernel/debug/dcc/../3/config_read

    /* Enable DCC */
    echo 1 > /sys/kernel/debug/dcc/../3/enable

    /* Run the timestamp test for working case */

    /* Send SW trigger */
    echo 1 > /sys/kernel/debug/dcc/../trigger

    /* Read SRAM */
    cat /dev/dcc_sram > dcc_sram1.bin

    /* Run the timestamp test for non-working case */

    /* Send SW trigger */
    echo 1 > /sys/kernel/debug/dcc/../trigger

    /* Read SRAM */
    cat /dev/dcc_sram > dcc_sram2.bin

    Get the parser from [1] and checkout the latest branch.

    /* Parse the SRAM bin */
    python dcc_parser.py -s dcc_sram1.bin --v2 -o output/
    python dcc_parser.py -s dcc_sram2.bin --v2 -o output/

    Sample parsed output of dcc_sram1.bin:

    <hwioDump version="1">
    <timestamp>03/14/21</timestamp>
    <generator>Linux DCC Parser</generator>
    <chip name="None" version="None">
    <register address="0x0010c004" value="0x80000000" />
    <register address="0x0010c008" value="0x00000008" />
    <register address="0x0010c00c" value="0x80004220" />
    <register address="0x0010c010" value="0x80000000" />
    </chip>
    <next_ll_offset>next_ll_offset : 0x1c </next_ll_offset>
    </hwioDump>

    ii)NOC register errors

    A particular class of registers called NOC which are functional registers was reporting
    errors while logging the values.To trace these errors the DCC has been used effectively.
    The steps followed were similar to the ones mentioned above.
    In addition to NOC registers a few other dependent registers were configured in DCC to
    monitor it's values during a crash. A look at the dependent register values revealed that
    the crash was happening due to a secured access to one of these dependent registers.
    All these debugging activity and finding the root cause was achieved using DCC.

    DCC parser is available at the following open source location

    https://source.codeaurora.org/quic/la/platform/vendor/qcom-opensource/tools/tree/dcc_parser

    Changes in V8

    *The DCC interface for debugfs has been changed as per comments on v7.
    The new interface details are documented in Documentation/ABI/testing/debugfs-driver-dcc.

    Souradeep Chowdhury (7):
    dt-bindings: Added the yaml bindings for DCC
    soc: qcom: dcc:Add driver support for Data Capture and Compare
    unit(DCC)
    MAINTAINERS: Add the entry for DCC(Data Capture and Compare) driver
    support
    arm64: dts: qcom: sm8150: Add Data Capture and Compare(DCC) support
    node
    arm64: dts: qcom: sc7280: Add Data Capture and Compare(DCC) support
    node
    arm64: dts: qcom: sc7180: Add Data Capture and Compare(DCC) support
    node
    arm64: dts: qcom: sdm845: Add Data Capture and Compare(DCC) support
    node

    Documentation/ABI/testing/debugfs-driver-dcc | 95 ++
    .../devicetree/bindings/arm/msm/qcom,dcc.yaml | 43 +
    MAINTAINERS | 8 +
    arch/arm64/boot/dts/qcom/sc7180.dtsi | 6 +
    arch/arm64/boot/dts/qcom/sc7280.dtsi | 6 +
    arch/arm64/boot/dts/qcom/sdm845.dtsi | 6 +
    arch/arm64/boot/dts/qcom/sm8150.dtsi | 6 +
    drivers/soc/qcom/Kconfig | 8 +
    drivers/soc/qcom/Makefile | 1 +
    drivers/soc/qcom/dcc.c | 1359 ++++++++++++++++++++
    10 files changed, 1538 insertions(+)
    create mode 100644 Documentation/ABI/testing/debugfs-driver-dcc
    create mode 100644 Documentation/devicetree/bindings/arm/msm/qcom,dcc.yaml
    create mode 100644 drivers/soc/qcom/dcc.c

    --
    2.7.4

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