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charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 6/28/2023 3:53 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: > > > 03/14/21 > Linux DCC Parser > > > > > > > next_ll_offset : 0x1c > > > 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 > > Changes in v25 > > * Updated the documentation of the structure dcc_config_entry as per the comments in V23 > * Updated the documentation of the dcc Kconfig definition as per comment in V24 > * Used u64 where applicable > * Removed the mutex locks where it is not needed > * Removed the use of unlikely keyword > * Renamed "nr_link_list" to "max_link_list" > > 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 | 8 + > drivers/misc/Makefile | 1 + > drivers/misc/qcom-dcc.c | 1312 +++++++++++++++++ > 6 files changed, 1378 insertions(+), 5 deletions(-) > create mode 100644 Documentation/devicetree/bindings/misc/qcom,dcc.yaml > create mode 100644 drivers/misc/qcom-dcc.c Gentle Ping _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel