Hi

I have had a look at a few of the patches. The buffer swap mechanism appears to be good.

However there is a lot of byte-ctr code in the "core" tmc / etr source files. As much of this code as possible needs to be moved to the byte-cntr specifc source.

I suggest having a helper function such as qcom_byte_ctr_in_use() to call from the core code, and if true then call back into the byte-cntr specific code to do the specialist functionality.

One other possibility is to have a flag / enum in the tmc->drvdata structure to indicate a variant. - e.g. TMC_STD, TMC_QCOM_BYTE_CTR, set at initialisation stage to remove the need for checking the device tree every call.

Regards

Mike

On Mon, 14 Jul 2025 at 07:31, Jie Gan jie.gan@oss.qualcomm.com wrote:

The byte-cntr function provided by the CTCU device is used to count the trace data entering the ETR. An interrupt is triggered if the data size exceeds the threshold set in the BYTECNTRVAL register. The interrupt handler counts the number of triggered interruptions.

Based on this concept, the irq_cnt can be used to determine whether the etr_buf is full. The ETR device will be disabled when the active etr_buf is nearly full or a timeout occurs. The nearly full buffer will be switched to background after synced. A new buffer will be picked from the etr_buf_list, then restart the ETR device.

The byte-cntr reading functions can access data from the synced and deactivated buffer, transferring trace data from the etr_buf to userspace without stopping the ETR device.

The byte-cntr read operation has integrated with the file node tmc_etr, for example: /dev/tmc_etr0 /dev/tmc_etr1

There are two scenarios for the tmc_etr file node with byte-cntr function:

1. BYTECNTRVAL register is configured and byte-cntr is enabled -> byte-cntr read
2. BYTECNTRVAL register is reset or byte-cntr is disabled -> original behavior

Shell commands to enable byte-cntr reading for etr0: echo 0x10000 > /sys/bus/coresight/devices/ctcu0/irq_val echo 1 > /sys/bus/coresight/devices/tmc_etr0/enable_sink echo 1 > /sys/bus/coresight/devices/etm0/enable_source cat /dev/tmc_etr0

Reset the BYTECNTR register for etr0: echo 0 > /sys/bus/coresight/devices/ctcu0/irq_val

Changes in V3 resend:

1. rebased on next-20250711.

Link to V3 - https://lore.kernel.org/all/20250624060438.7469-1-jie.gan@oss.qualcomm.com/

Changes in V3:

1. The previous solution has been deprecated.
2. Add a etr_buf_list to manage allcated etr buffers.
3. Add a logic to switch buffer for ETR.
4. Add read functions to read trace data from synced etr buffer.

Link to V2 - https://lore.kernel.org/all/20250410013330.3609482-1-jie.gan@oss.qualcomm.co...

Changes in V2:

1. Removed the independent file node /dev/byte_cntr.
2. Integrated the byte-cntr's file operations with current ETR file node.
3. Optimized the driver code of the CTCU that associated with byte-cntr.
4. Add kernel document for the export API tmc_etr_get_rwp_offset.
5. Optimized the way to read the rwp_offset according to Mike's suggestion.
6. Removed the dependency of the dts patch.

Link to V1 - https://lore.kernel.org/all/20250310090407.2069489-1-quic_jiegan@quicinc.com...

Jie Gan (10): coresight: core: Refactoring ctcu_get_active_port and make it generic coresight: core: add a new API to retrieve the helper device dt-bindings: arm: add an interrupt property for Coresight CTCU coresight: ctcu: enable byte-cntr for TMC ETR devices coresight: tmc: add etr_buf_list to store allocated etr_buf coresight: tmc: add create/delete functions for etr_buf_node coresight: tmc: add prepare/unprepare functions for byte-cntr coresight: tmc: add a switch buffer function for byte-cntr coresight: tmc: add read function for byte-cntr arm64: dts: qcom: sa8775p: Add interrupts to CTCU device

.../testing/sysfs-bus-coresight-devices-ctcu | 5 + .../bindings/arm/qcom,coresight-ctcu.yaml | 17 ++ arch/arm64/boot/dts/qcom/sa8775p.dtsi | 5 + drivers/hwtracing/coresight/Makefile | 2 +- drivers/hwtracing/coresight/coresight-core.c | 54 ++++ .../coresight/coresight-ctcu-byte-cntr.c | 102 +++++++ .../hwtracing/coresight/coresight-ctcu-core.c | 113 ++++++-- drivers/hwtracing/coresight/coresight-ctcu.h | 49 +++- drivers/hwtracing/coresight/coresight-priv.h | 4 + .../hwtracing/coresight/coresight-tmc-core.c | 70 ++++- .../hwtracing/coresight/coresight-tmc-etr.c | 270 ++++++++++++++++++ drivers/hwtracing/coresight/coresight-tmc.h | 29 ++ 12 files changed, 688 insertions(+), 32 deletions(-) create mode 100644 Documentation/ABI/testing/sysfs-bus-coresight-devices-ctcu create mode 100644 drivers/hwtracing/coresight/coresight-ctcu-byte-cntr.c

-- 2.34.1