Hi

On Fri, 16 Apr 2021 at 15:16, taozha@codeaurora.org wrote:

On 2021-04-16 19:23, Alexander Shishkin wrote:

...

Tao Zhang taozha@codeaurora.org writes:

...

Add property "coresight-name" for coresight component name. This allows coresight driver to read device name from device entries.

Signed-off-by: Tao Zhang taozha@codeaurora.org

Documentation/devicetree/bindings/arm/coresight.txt | 2 ++ 1 file changed, 2 insertions(+)

diff --git a/Documentation/devicetree/bindings/arm/coresight.txt b/Documentation/devicetree/bindings/arm/coresight.txt index d711676..0e980ce 100644 --- a/Documentation/devicetree/bindings/arm/coresight.txt +++ b/Documentation/devicetree/bindings/arm/coresight.txt @@ -103,6 +103,8 @@ its hardware characteristcs. powers down the coresight component also powers down and loses its context. This property is currently only used for the ETM 4.x driver.

• • coresight-name: the name of the coresight devices.

Which devices? Also, is it a common practice to extend device tree definitions based on arbitrary driver needs, or should there be some sort of a discussion first?

Regards,

Alex

Through the device tree entries, we can define their own name for any coresight device. This design is mainly used to facilitate the unified naming of coresight devgies across targets. e.g, without this patch, we can only see from sysFS there are multiple funnels, but we cannot know which funnel it is based on their names from sysFS. After applying this patch, we can directly know what device it is by observing the device name in sysFS. And the common scripts can be developed, since applying this patch, the same coresight device can have the same name across targets. Each developer or vendor can define the name of each coresight device according to their preferences and products.

Tao

1) I am concerned that this will break the existing protocol which associates a fixed device type name + number with each device - i.e. etm0, funnel1 etc. This naming convention allows for generic common scripts to be developed - see: ./tools/perf/tests/shel/test_arm_coresight.sh This relies on the device type prefixes to iterate across all devices in a system - and uses the connections links that are present in each of the devices to determine the topology. Replacing these with arbitrary names will break existing scripts.

2) Using the current system it is entirely possible to determine which specific device a given name relates to. e.g. ls -al /sys/bus/coresight/devices/

lrwxrwxrwx 1 root root 0 Apr 14 19:02 cti_cpu0 -> ../../../devices/platform/soc/858000.cti/cti_cpu0 lrwxrwxrwx 1 root root 0 Apr 14 19:02 cti_cpu1 -> ../../../devices/platform/soc/859000.cti/cti_cpu1 lrwxrwxrwx 1 root root 0 Apr 14 19:02 cti_cpu2 -> ../../../devices/platform/soc/85a000.cti/cti_cpu2 lrwxrwxrwx 1 root root 0 Apr 14 19:02 cti_cpu3 -> ../../../devices/platform/soc/85b000.cti/cti_cpu3 lrwxrwxrwx 1 root root 0 Apr 14 19:02 cti_sys0 -> ../../../devices/platform/soc/810000.cti/cti_sys0 lrwxrwxrwx 1 root root 0 Apr 14 19:02 cti_sys1 -> ../../../devices/platform/soc/811000.cti/cti_sys1 lrwxrwxrwx 1 root root 0 Apr 14 19:02 etm0 -> ../../../devices/platform/soc/85c000.etm/etm0 lrwxrwxrwx 1 root root 0 Apr 14 19:02 etm1 -> ../../../devices/platform/soc/85d000.etm/etm1 lrwxrwxrwx 1 root root 0 Apr 14 19:02 etm2 -> ../../../devices/platform/soc/85e000.etm/etm2 lrwxrwxrwx 1 root root 0 Apr 14 19:02 etm3 -> ../../../devices/platform/soc/85f000.etm/etm3 lrwxrwxrwx 1 root root 0 Apr 16 14:17 funnel0 -> ../../../devices/platform/soc/821000.funnel/funnel0 lrwxrwxrwx 1 root root 0 Apr 16 14:17 funnel1 -> ../../../devices/platform/soc/841000.funnel/funnel1 lrwxrwxrwx 1 root root 0 Apr 16 14:17 replicator0 -> ../../../devices/platform/soc/824000.replicator/replicator0 lrwxrwxrwx 1 root root 0 Apr 16 14:17 tmc_etf0 -> ../../../devices/platform/soc/825000.etf/tmc_etf0 lrwxrwxrwx 1 root root 0 Apr 16 14:17 tmc_etr0 -> ../../../devices/platform/soc/826000.etr/tmc_etr0 lrwxrwxrwx 1 root root 0 Apr 16 14:17 tpiu0 -> ../../../devices/platform/soc/820000.tpiu/tpiu

Further topology can be determined using the connections sub-directory in each device:-

ls -al /sys/bus/coresight/devices/etm0/connections/out:0 lrwxrwxrwx 1 root root 0 Apr 16 14:18 /sys/bus/coresight/devices/etm0/connections/out:0 -> ../../../841000.funnel/funnel1

Using this information it is possible to iterate across the entire topology of any coresight system.

3) If there is some scripting requirement that cannot be solved with the information available above - then it would be better to add this name as an alias rather than a direct replacement. Therefore any coresight device could have an alias_name entry, that could be interrogated by a script and used as required. This avoids breaking any existing scripts using the established naming convention.

4) Any devicetree attribute should follow the <owner>,<attribute> naming convention. e.g. arm,some_attribute. I agree with Alex that it may not be normal practice to add in attributes in these circumstances - this does not appear to relate to a specific hardware feature or limitation. You may wish to discuss this with the device tree maintainers.

Thanks and Regards

Mike