[PATCH V23 0/3] misc: Add driver support for Data Capture and Compare unit(DCC)

[Souradeep Chowdhury]

On 5/5/2023 12:06 PM, Souradeep Chowdhury wrote:
> 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/qcom-dcc/../3/config
> echo R 0x10c008 > /sys/kernel/debug/qcom-dcc/../3/config
> echo R 0x10c00c > /sys/kernel/debug/qcom-dcc/../3/config
> echo R 0x10c010 > /sys/kernel/debug/qcom-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/qcom-dcc/../3/config_read
> 
> /* Enable DCC */
> echo 1 > /sys/kernel/debug/qcom-dcc/../3/enable
> 
> /* Run the timestamp test for working case */
> 
> /* Send SW trigger */
> echo 1 > /sys/kernel/debug/qcom-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/qcom-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://git.codelinaro.org/clo/le/platform/vendor/qcom-opensource/tools/-/tree/opensource-tools.lnx.1.0.r176-rel/dcc_parser
> 
> Souradeep Chowdhury (3):
>    dt-bindings: misc: qcom,dcc: Add the dtschema
>    misc: dcc: Add driver support for Data Capture and Compare unit(DCC)
>    MAINTAINERS: Add the entry for DCC(Data Capture and Compare) driver
>      support
> 
>   Documentation/ABI/testing/debugfs-driver-dcc  |   10 +-
>   .../devicetree/bindings/misc/qcom,dcc.yaml    |   44 +
>   MAINTAINERS                                   |    8 +
>   drivers/misc/Kconfig                          |    9 +
>   drivers/misc/Makefile                         |    1 +
>   drivers/misc/qcom-dcc.c                       | 1325 +++++++++++++++++
>   6 files changed, 1392 insertions(+), 5 deletions(-)
>   create mode 100644 Documentation/devicetree/bindings/misc/qcom,dcc.yaml
>   create mode 100644 drivers/misc/qcom-dcc.c
> 

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