Hi
On 05/11/2026 12:19, Songwei.Chai wrote:
Hi Suzuki,
I wanted to follow up and see if you might have some time to take a look at this patch.
Apologies for the delay in responding on this one. But I have now reviewed the series, please address the comments and repost them based on 7.4-rcX
Cheers Suzuki
We’d really appreciate any feedback you may have, as it would help us determine the next steps and move this work forward. Thanks for your time.
Best regards, Songwei
On 7/30/2026 4:06 PM, Songwei Chai wrote:
From: Songwei Chai songchai@qti.qualcomm.com
We propose creating a new qcom directory under drivers/hwtracing to host this TGU driver, as well as additional Qualcomm-specific hwtracing drivers that we plan to submit in the coming months. This structure will help organize vendor-specific implementations and facilitate future development and maintenance.
Feedback from the community on this proposal is highly appreciated.
- Why we are proposing this:
TGU has the ability to monitor signal conditions and trigger debug- related actions, serving as a programmable hardware component that enhances system trace and debug capabilities. Placing it under drivers/hwtracing aligns with its function as a trace generation utility.
We previously attempted to push this driver to drivers/hwtracing/ coresight, but did not receive support from the maintainers of the CoreSight subsystem. The reason provided was: “This component is primarily a part of the Qualcomm proprietary QPMDA subsystem, and is capable of operating independently from the CoreSight hardware trace generation system.”
Chat history : https://lore.kernel.org/all/ CAJ9a7ViKxHThyZfFFDV_FkNRimk4uo1NrMtQ-kcaj1qO4ZcGnA@mail.gmail.com/
Given this, we have been considering whether it would be appropriate to create a dedicated drivers/hwtracing/qcom directory for Qualcomm-related hwtracing drivers. This would follow the precedent set by Intel, which maintains its own directory at drivers/hwtracing/ intel_th. We believe this structure would significantly facilitate future submissions of related Qualcomm drivers.
- Maintenance of drivers/hwtracing/qcom:
Bjorn, who maintains linux-arm-msm, will be the maintainer of this directory — we’ve discussed this with him and he’s aware that his task list may grow accordingly. Additionally, Qualcomm engineers familiar with the debug hardware — such as [Tingwei Zhang, Jinlong Mao, Songwei Chai], will be available to review incoming patches and support ongoing development.
- Detail for TGU:
This component can be utilized to sense a plurality of signals and create a trigger into the CTI or generate interrupts to processors once the input signal meets the conditions. We can treat the TGU’s workflow as a flowsheet, it has some “steps” regions for customization. In each step region, we can set the signals that we want with priority in priority_group, set the conditions in each step via condition_decode, and set the resultant action by condition_select. Meanwhile, some TGUs (not all) also provide timer/counter functionality. Based on the characteristics described above, we consider the TGU as a helper in the CoreSight subsystem. Its master device is the TPDM, which can transmit signals from other subsystems, and we reuse the existing ports mechanism to link the TPDM to the connected TGU.
Here is a detailed example to explain how to use the TGU:
In this example, the TGU is configured to use 2 conditions, 2 steps, and the timer. The goal is to look for one of two patterns which are generated from TPDM, giving priority to one, and then generate a trigger once the timer reaches a certain value. In other words, two conditions are used for the first step to look for the two patterns, where the one with the highest priority is used in the first condition. Then, in the second step, the timer is enabled and set to be compared to the given value at each clock cycle. These steps are better shown below. |-----------------| | | | TPDM | | | |-----------------| | | --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- ---
| | | | | |--------------------| | | |---- ---> | | Go to next steps | | | | | |--- ---> | Enable timer | | | | v | | | | | | |-----------------| | |--------------------| | | | | | Yes | | | | | | inputs==0xB | ----->| | <-------- | | | | | | | No | | | No | |-----------------| | v | | | | | | |-----------------| | | | | | | | | | | | | | | | timer>=3 |-- | | | v | | | | | | |-----------------| | |-----------------| | | | | | Yes | | | | |--- | inputs==0xA | ----->| | Yes | | | | | | | |-----------------| v | | |-----------------| | | | | | | | Trigger | | | | | | | |-----------------| | | TGU | | |--- --- --- --- --- --- --- --- --- --- --- --- --- --- |--- --- -- | | v |-----------------| |The controllers | |which will use | |triggers further | |-----------------|
steps: 1. Reset TGU /*it will disable tgu and reset dataset*/ - echo 1 > /sys/bus/amba/devices/<tgu-name>/reset_tgu
2. Set the pattern match for priority0 to 0xA = 0b1010 and for priority 1 to 0xB = 0b1011. - echo 0x11113232 > /sys/bus/amba/devices/<tgu-name>/ step0_priority0/reg0 - echo 0x11113233 > /sys/bus/amba/devices/<tgu-name>/ step0_priority1/reg0
Note: Bit distribution diagram for each priority register |-------------------------------------------------------------------| | Bits | Field Nam | Description | |-------------------------------------------------------------------| | | | 00 = bypass for OR output | | 29:28 | SEL_BIT7_TYPE2 | 01 = bypass for AND output | | | | 10 = sense input '0' is true| | | | 11 = sense input '1' is true| |-------------------------------------------------------------------| | | | 00 = bypass for OR output | | 25:24 | SEL_BIT6_TYPE2 | 01 = bypass for AND output | | | | 10 = sense input '0' is true| | | | 11 = sense input '1' is true| |-------------------------------------------------------------------| | | | 00 = bypass for OR output | | 21:20 | SEL_BIT5_TYPE2 | 01 = bypass for AND output | | | | 10 = sense input '0' is true| | | | 11 = sense input '1' is true| |-------------------------------------------------------------------| | | | 00 = bypass for OR output | | 17:16 | SEL_BIT4_TYPE2 | 01 = bypass for AND output | | | | 10 = sense input '0' is true| | | | 11 = sense input '1' is true| |-------------------------------------------------------------------| | | | 00 = bypass for OR output | | 13:12 | SEL_BIT3_TYPE2 | 01 = bypass for AND output | | | | 10 = sense input '0' is true| | | | 11 = sense input '1' is true| |-------------------------------------------------------------------| | | | 00 = bypass for OR output | | 9:8 | SEL_BIT2_TYPE2 | 01 = bypass for AND output | | | | 10 = sense input '0' is true| | | | 11 = sense input '1' is true| |-------------------------------------------------------------------| | | | 00 = bypass for OR output | | 5:4 | SEL_BIT1_TYPE2 | 01 = bypass for AND output | | | | 10 = sense input '0' is true| | | | 11 = sense input '1' is true| |-------------------------------------------------------------------| | | | 00 = bypass for OR output | | 1:0 | SEL_BIT0_TYPE2 | 01 = bypass for AND output | | | | 10 = sense input '0' is true| | | | 11 = sense input '1' is true| |-------------------------------------------------------------------| These bits are used to identify the signals we want to sense, with a maximum signal number of 140. For example, to sense the signal 0xA (binary 1010), we set the value of bits 0 to 13 to 3232, which represents 1010. The remaining bits are set to 1, as we want to use AND gate to summarize all the signals we want to sense here. For rising or falling edge detection of any input to the priority, set the remaining bits to 0 to use an OR gate.
3. look for the pattern for priority_i i=0,1. - echo 0x3 > /sys/bus/amba/devices/<tgu-name>/ step0_condition_decode/reg0 - echo 0x30 > /sys/bus/amba/devices/<tgu-name>/ step0_condition_decode/reg1
|-------------------------------------------------------------------------------| | Bits | Field Nam | Description | |-------------------------------------------------------------------------------| | | |For each decoded condition, this | | 24 | NOT |inverts the output. If the condition | | | |decodes to true, and the NOT field | | | |is '1', then the output is NOT true. | |-------------------------------------------------------------------------------| | | |When '1' the output from the associated| | 21 | BC0_COMP_ACTIVE |comparator will be actively included in| | | |the decoding of this particular | | | | condition. | |-------------------------------------------------------------------------------| | | |When '1' the output from the associated| | | |comparator will need to be 1 to affect | | 20 | BC0_COMP_HIGH |the decoding of this condition. | | | |Conversely, a '0' here requires a '0' | | | |from the comparator | |-------------------------------------------------------------------------------| | | |When '1' the output from the associated| | 17 | |comparator will be actively included in| | | TC0_COMP_ACTIVE |the decoding of this particular | | | | condition. | |-------------------------------------------------------------------------------| | | |When '1' the output from the associated| | | |comparator will need to be 1 to affect | | 16 | TC0_COMP_HIGH |the decoding of this particular | | | |condition.Conversely, a 0 here | | | |requires a '0' from the comparator | |-------------------------------------------------------------------------------| | | |When '1' the output from Priority_n | | | |OR logic will be actively | | 4n+3 | Priority_n_OR_ACTIVE|included in the decoding of | | | (n=0,1,2,3) |this particular condition. | | | | | |-------------------------------------------------------------------------------| | | |When '1' the output from Priority_n | | | |will need to be '1' to affect the | | 4n+2 | Priority_n_OR_HIGH |decoding of this particular | | | (n=0,1,2,3) |condition. Conversely, a '0' here | | | |requires a '0' from Priority_n OR logic| |-------------------------------------------------------------------------------| | | |When '1' the output from Priority_n | | | |AND logic will be actively | | 4n+1 |Priority_n_AND_ACTIVE|included in the decoding of this | | | (n=0,1,2,3) |particular condition. | | | | | |-------------------------------------------------------------------------------| | | |When '1' the output from Priority_n | | | |AND logic will need to be '1' to | | 4n | Priority_n_AND_HIGH |affect the decoding of this | | | (n=0,1,2,3) |particular condition. Conversely, | | | |a '0' here requires a '0' from | | | |Priority_n AND logic. | |-------------------------------------------------------------------------------| Since we use `priority_0` and `priority_1` with an AND output in step 2, we set `0x3` and `0x30` here to activate them.
4. Set NEXT_STEP = 1 and TC0_ENABLE = 1 so that when the conditions are met then the next step will be step 1 and the timer will be enabled. - echo 0x20008 > /sys/bus/amba/devices/<tgu-name>/ step0_condition_select/reg0 - echo 0x20008 > /sys/bus/amba/devices/<tgu-name>/ step0_condition_select/reg1
|-----------------------------------------------------------------------------| | Bits | Field Nam | Description | |-----------------------------------------------------------------------------| | | |This field defines the next step the | | 18:17 | NEXT_STEP |TGU will 'goto' for the associated | | | |Condition and Step. | |-----------------------------------------------------------------------------| | | |For each possible output trigger | | 13 | TRIGGER |available, set a '1' if you want | | | |the trigger to go active for the | | | |associated condition and Step. | |-----------------------------------------------------------------------------| | | |This will cause BC0 to increment if the| | 9 | BC0_INC |associated Condition is decoded for | | | |this step. | |-----------------------------------------------------------------------------| | | |This will cause BC0 to decrement if the| | 8 | BC0_DEC |associated Condition is decoded for | | | |this step. | |-----------------------------------------------------------------------------| | | |This will clear BC0 count value to 0 if| | 7 | BC0_CLEAR |the associated Condition is decoded | | | |for this step. | |-----------------------------------------------------------------------------| | | |This will cause TC0 to increment until | | 3 | TC0_ENABLE |paused or cleared if the associated | | | |Condition is decoded for this step. | |-----------------------------------------------------------------------------| | | |This will cause TC0 to pause until | | 2 | TC0_PAUSE |enabled if the associated Condition | | | |is decoded for this step. | |-----------------------------------------------------------------------------| | | |This will clear TC0 count value to 0 | | 1 | TC0_CLEAR |if the associated Condition is | | | |decoded for this step. | |-----------------------------------------------------------------------------| | | |This will set the done signal to the | | 0 | DONE |TGU FSM if the associated Condition | | | |is decoded for this step. | |-----------------------------------------------------------------------------| Based on the distribution diagram, we set `0x20008` for `priority0` and `priority1` to achieve "jump to step 1 and enable TC0" once the signal is sensed.
5. activate the timer comparison for this step. - echo 0x30000 > /sys/bus/amba/devices/<tgu-name>/ step1_condition_decode/reg0
|-------------------------------------------------------------------------------| | | |When '1' the output from the associated| | 17 | |comparator will be actively included in| | | TC0_COMP_ACTIVE |the decoding of this particular | | | | condition. | |-------------------------------------------------------------------------------| | | |When '1' the output from the associated| | | |comparator will need to be 1 to affect | | 16 | TC0_COMP_HIGH |the decoding of this particular | | | |condition.Conversely, a 0 here | | | |requires a '0' from the comparator | |-------------------------------------------------------------------------------| Accroding to the decode distribution diagram , we give 0x30000 here to set 16th&17th bit to enable timer comparison.
6. Set the NEXT_STEP = 0 and TC0_PAUSE = 1 and TC0_CLEAR = 1 once the timer has reached the given value. - echo 0x6 > /sys/bus/amba/devices/<tgu-name>/ step1_condition_select/reg0
7. Enable Trigger 0 for TGU when the condition 0 is met in step1, i.e. when the timer reaches 3. - echo 0x2000 > /sys/bus/amba/devices/<tgu-name>/ step1_condition_select/default
Note: 1. 'default' register allows for establishing the resultant action for the default condition
2. Trigger:For each possible output trigger available from the Design document, there are three triggers: interrupts, CTI, and Cross-TGU mapping.All three triggers can occur, but the choice of which trigger to use depends on the user's needs.
8. Compare the timer to 3 in step 1. - echo 0x3 > /sys/bus/amba/devices/<tgu-name>/step1_timer/reg0
9. enale tgu - echo 1 > /sys/bus/amba/devices/<tgu-name>/enable_tgu
Link to V15: https://lore.kernel.org/all/20260701055529.445819-1- songwei.chai@oss.qualcomm.com/
Changes in V16:
- Fixed enable/disable race and PM refcount handling.
- Fixed sysfs exposure before driver initialization.
- Fixed priority allocation and access races.
- Fixed uninitialized return value in condition decode.
- Fixed sysfs attribute naming collision issues.
- Added ABI documentation for the default node.
Link to V14: https://lore.kernel.org/all/20260417073336.2712426-1- songwei.chai@oss.qualcomm.com/
Changes in V15:
- Add a maintainer for "drivers/hwtracing/qcom" in MAINTAINERS
Link to V13: https://lore.kernel.org/all/20260402092838.341295-1- songwei.chai@oss.qualcomm.com/
Changes in V14:
- Fix some typos and formatting.
Link to V12: https://lore.kernel.org/all/20260317032639.2393221-1- songwei.chai@oss.qualcomm.com/
Changes in V13:
- add ":" after "KernelVersion"
- add an enablement check in the enable function to avoid increasing
the counter each time
Link to V11: https://lore.kernel.org/all/ee1ca8e6-8e5f-47d8-8a24- f904ee2fc6d0@oss.qualcomm.com/
Changes in V12:
- Remove the in-ports property from the bindings, as this device is
decoupled from CoreSight.
- Update kernel version and date.
Link to V10: https://lore.kernel.org/ all/20c5406d-3e9f-4fdb-84ba-4cbe629c79b5@oss.qualcomm.com/
Changes in V11:
- Change the names of members in drvdata: max_xxx -> num_xxx, enable -
enabled
- Use "FIELD_GET" to replace "BMVAL"
- Use devm_kcalloc to replace devm_kzalloc once create members of
value_table
- Keep a consistent \n above return
- Keep reverse-Christmas-tree style
- Add checks so that the enable and reset nodes only accept 0 or 1
Link to V9: https://lore.kernel.org/all/20251219065902.2296896-1- songwei.chai@oss.qualcomm.com/
Changes in V10:
- Modified code formatting based on Jie's feedback to improve
readability.
- Applied inverse Christmas tree order to the variables.
Link to V8: https://lore.kernel.org/all/20251203090055.2432719-1- songwei.chai@oss.qualcomm.com/
Changes in V9:
- Decoupled the tgu driver from coresight header file and registered
it as an amba device.
- Retained Rob's reviewed-by tag on patch1/7 since the file remains
unchanged.
- Updated the sysfs node path in the Documentation directory.
Link to V7: https://lore.kernel.org/all/20251104064043.88972-1- songwei.chai@oss.qualcomm.com/
Changes in V8:
- Add "select" section in bindings.
- Update publish date in "sysfs-bus-coresight-devices-tgu".
Link to V6: https://lore.kernel.org/all/20250709104114.22240-1- songchai@qti.qualcomm.com/
Changes in V7:
- Move the TGU code location from 'drivers/hwtracing/coresight/' to
'drivers/hwtracing/qcom/'.
- Rename the spinlock used in the code from 'spinlock' to 'lock'.
- Perform the 'calculate_array_location' separately, instead of doing
it within the function.
- Update the sender email address.
Link to V5: https://lore.kernel.org/all/20250529081949.26493-1- quic_songchai@quicinc.com/
Changes in V6:
- Replace spinlock with guard(spinlock) in tgu_enable.
- Remove redundant blank line.
- Update publish date and contact member's name in "sysfs-bus-
coresight-devices-tgu".
Link to V4: https://patchwork.kernel.org/project/linux-arm-msm/ cover/20250423101054.954066-1-quic_songchai@quicinc.com/
Changes in V5:
- Update publish date and kernel_version in "sysfs-bus-coresight-
devices-tgu"
Link to V3: https://lore.kernel.org/all/20250227092640.2666894-1- quic_songchai@quicinc.com/
Changes in V4:
- Add changlog in coverletter.
- Correct 'year' in Copyright in patch1.
- Correct port mechansim description in patch1.
- Remove 'tgu-steps','tgu-regs','tgu-conditions','tgu-timer-counters'
from dt-binding and set them through reading DEVID register as per Mike's suggestion.
- Modify tgu_disable func to make it have single return point in
patch2 as per Mike's suggestion.
- Use sysfs_emit in enable_tgu_show func in ptach2.
- Remove redundant judgement in enable_tgu_store in patch2.
- Correct typo in description in patch3.
- Set default ret as SYSFS_GROUP_INVISIBLE, and returnret at end in
pacth3 as per Mike's suggestion.
- Remove tgu_dataset_ro definition in patch3
- Use #define constants with explanations of what they are rather than
arbitrary magic numbers in patch3 and patch4.
- Check -EINVAL before using 'calculate_array_location()' in array in
patch4.
- Add 'default' in 'tgu_dataset_show''s switch part in patch4.
- Document the value needed to initiate the reset in pacth7.
- Check "value" in 'reset_tgu_store' and bail out with an error code
if 0 in patch7.
- Remove dev_dbg in 'reset_tgu_store' in patch7.
Link to V2: https://lore.kernel.org/all/20241010073917.16023-1- quic_songchai@quicinc.com/
Changes in V3:
- Correct typo and format in dt-binding in patch1
- Rebase to the latest kernel version
Link to V1: https://lore.kernel.org/all/20240830092311.14400-1- quic_songchai@quicinc.com/
Changes in V2: - Use real name instead of login name, - Correct typo and format in dt-binding and code. - Bring order in tgu_prob(declarations with and without assignments) as per Krzysztof's suggestion. - Add module device table in patch2. - Set const for tgu_common_grp and tgu_ids in patch2. - Initialize 'data' in tgu_ids to fix the warning in pacth2.
Songwei Chai (7): dt-bindings: arm: Add support for Qualcomm TGU trace qcom-tgu: Add TGU driver qcom-tgu: Add signal priority support qcom-tgu: Add TGU decode support qcom-tgu: Add support to configure next action qcom-tgu: Add timer/counter functionality for TGU qcom-tgu: Add reset node to initialize
.../ABI/testing/sysfs-bus-amba-devices-tgu | 60 ++ .../devicetree/bindings/arm/qcom,tgu.yaml | 71 ++ MAINTAINERS | 11 + drivers/Makefile | 1 + drivers/hwtracing/Kconfig | 2 + drivers/hwtracing/qcom/Kconfig | 20 + drivers/hwtracing/qcom/Makefile | 3 + drivers/hwtracing/qcom/tgu.c | 782 ++++++++++++++++++ drivers/hwtracing/qcom/tgu.h | 318 +++++++ 9 files changed, 1268 insertions(+) create mode 100644 Documentation/ABI/testing/sysfs-bus-amba-devices-tgu create mode 100644 Documentation/devicetree/bindings/arm/qcom,tgu.yaml create mode 100644 drivers/hwtracing/qcom/Kconfig create mode 100644 drivers/hwtracing/qcom/Makefile create mode 100644 drivers/hwtracing/qcom/tgu.c create mode 100644 drivers/hwtracing/qcom/tgu.h