Re: [PATCH v2] Documentation: coresight: Update the generic device names

[Mathieu Poirier]

On Mon, 10 Jun 2019 at 12:02, Suzuki K Poulose <suzuki.poulose@xxxxxxx> wrote:
>
> Update the documentation to reflect the new naming scheme with
> latest changes.
>
> Reported-by: Leo Yan <leo.yan@xxxxxxxxxx>
> Cc: Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>
> Cc: Jonathan Corbet <corbet@xxxxxxx>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> ---
> Changes since v1
>   - Add a section about the Device Naming scheme and add refer to
>     it in the examples.
> ---
>  Documentation/trace/coresight.txt | 82 ++++++++++++++++++++++++++++++++-------
>  1 file changed, 67 insertions(+), 15 deletions(-)
>
> diff --git a/Documentation/trace/coresight.txt b/Documentation/trace/coresight.txt
> index efbc832..b027d61 100644
> --- a/Documentation/trace/coresight.txt
> +++ b/Documentation/trace/coresight.txt
> @@ -188,6 +188,49 @@ specific to that component only.  "Implementation defined" customisations are
>  expected to be accessed and controlled using those entries.
>
>
> +Device Naming scheme
> +------------------------
> +The devices that appear on the "coresight" bus were named the same as their
> +parent devices, i.e, the real devices that appears on AMBA bus or the platform bus.
> +Thus the names were based on the Linux Open Firmware layer naming convention,
> +which follows the base physical address of the device followed by the device
> +type. e.g:
> +
> +root:~# ls /sys/bus/coresight/devices/
> + 20010000.etf  20040000.funnel      20100000.stm     22040000.etm
> + 22140000.etm  230c0000.funnel      23240000.etm     20030000.tpiu
> + 20070000.etr  20120000.replicator  220c0000.funnel
> + 23040000.etm  23140000.etm         23340000.etm
> +
> +However, with the introduction of ACPI support, the names of the real
> +devices are a bit cryptic and non-obvious. Thus, a new naming scheme was
> +introduced to use more generic names based on the type of the device. The
> +following rules apply:
> +
> +  1) Devices that are bound to CPUs, are named based on the CPU logical
> +     number.
> +
> +     e.g, ETM bound to CPU0 is named "etm0"
> +
> +  2) All other devices follow a pattern, "<device_type_prefix>N", where :
> +
> +       <device_type_prefix>    - A prefix specific to the type of the device
> +       N                       - a sequential number assigned based on the order
> +                                 of probing.
> +
> +       e.g, tmc_etf0, tmc_etr0, funnel0, funnel1
> +
> +Thus, with the new scheme the devices could appear as :
> +
> +root:~# ls /sys/bus/coresight/devices/
> + etm0     etm1     etm2         etm3  etm4      etm5      funnel0
> + funnel1  funnel2  replicator0  stm0  tmc_etf0  tmc_etr0  tpiu0

This looks goo do me.  Jonathan, if you prefer to handle this via your tree:

Reviewed-by: Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>

Otherwise I'll pick it up.

Thanks,
Mathieu

> +
> +Some of the examples below might refer to old naming scheme and some
> +to the newer scheme, to give a confirmation that what you see on your
> +system is not unexpected. One must use the "names" as they appear on
> +the system under specified locations.
> +
>  How to use the tracer modules
>  -----------------------------
>
> @@ -326,16 +369,25 @@ amount of processor cores), the "cs_etm" PMU will be listed only once.
>  A Coresight PMU works the same way as any other PMU, i.e the name of the PMU is
>  listed along with configuration options within forward slashes '/'.  Since a
>  Coresight system will typically have more than one sink, the name of the sink to
> -work with needs to be specified as an event option.  Names for sink to choose
> -from are listed in sysFS under ($SYSFS)/bus/coresight/devices:
> +work with needs to be specified as an event option.
> +On newer kernels the available sinks are listed in sysFS under:
> +($SYSFS)/bus/event_source/devices/cs_etm/sinks/
>
> -       root@linaro-nano:~# ls /sys/bus/coresight/devices/
> -               20010000.etf   20040000.funnel  20100000.stm  22040000.etm
> -               22140000.etm  230c0000.funnel  23240000.etm 20030000.tpiu
> -               20070000.etr     20120000.replicator  220c0000.funnel
> -               23040000.etm  23140000.etm     23340000.etm
> +       root@localhost:/sys/bus/event_source/devices/cs_etm/sinks# ls
> +       tmc_etf0  tmc_etr0  tpiu0
>
> -       root@linaro-nano:~# perf record -e cs_etm/@20070000.etr/u --per-thread program
> +On older kernels, this may need to be found from the list of coresight devices,
> +available under ($SYSFS)/bus/coresight/devices/:
> +
> +       root:~# ls /sys/bus/coresight/devices/
> +        etm0     etm1     etm2         etm3  etm4      etm5      funnel0
> +        funnel1  funnel2  replicator0  stm0  tmc_etf0  tmc_etr0  tpiu0
> +
> +       root@linaro-nano:~# perf record -e cs_etm/@tmc_etr0/u --per-thread program
> +
> +As mentioned above in section "Device Naming scheme", the names of the devices could
> +look different from what is used in the example above. One must use the device names
> +as it appears under the sysFS.
>
>  The syntax within the forward slashes '/' is important.  The '@' character
>  tells the parser that a sink is about to be specified and that this is the sink
> @@ -352,7 +404,7 @@ perf can be used to record and analyze trace of programs.
>  Execution can be recorded using 'perf record' with the cs_etm event,
>  specifying the name of the sink to record to, e.g:
>
> -    perf record -e cs_etm/@20070000.etr/u --per-thread
> +    perf record -e cs_etm/@tmc_etr0/u --per-thread
>
>  The 'perf report' and 'perf script' commands can be used to analyze execution,
>  synthesizing instruction and branch events from the instruction trace.
> @@ -381,7 +433,7 @@ sort example is from the AutoFDO tutorial (https://gcc.gnu.org/wiki/AutoFDO/Tuto
>         Bubble sorting array of 30000 elements
>         5910 ms
>
> -       $ perf record -e cs_etm/@20070000.etr/u --per-thread taskset -c 2 ./sort
> +       $ perf record -e cs_etm/@tmc_etr0/u --per-thread taskset -c 2 ./sort
>         Bubble sorting array of 30000 elements
>         12543 ms
>         [ perf record: Woken up 35 times to write data ]
> @@ -405,7 +457,7 @@ than the program flow through the code.
>  As with any other CoreSight component, specifics about the STM tracer can be
>  found in sysfs with more information on each entry being found in [1]:
>
> -root@genericarmv8:~# ls /sys/bus/coresight/devices/20100000.stm
> +root@genericarmv8:~# ls /sys/bus/coresight/devices/stm0
>  enable_source   hwevent_select  port_enable     subsystem       uevent
>  hwevent_enable  mgmt            port_select     traceid
>  root@genericarmv8:~#
> @@ -413,14 +465,14 @@ root@genericarmv8:~#
>  Like any other source a sink needs to be identified and the STM enabled before
>  being used:
>
> -root@genericarmv8:~# echo 1 > /sys/bus/coresight/devices/20010000.etf/enable_sink
> -root@genericarmv8:~# echo 1 > /sys/bus/coresight/devices/20100000.stm/enable_source
> +root@genericarmv8:~# echo 1 > /sys/bus/coresight/devices/tmc_etf0/enable_sink
> +root@genericarmv8:~# echo 1 > /sys/bus/coresight/devices/stm0/enable_source
>
>  From there user space applications can request and use channels using the devfs
>  interface provided for that purpose by the generic STM API:
>
> -root@genericarmv8:~# ls -l /dev/20100000.stm
> -crw-------    1 root     root       10,  61 Jan  3 18:11 /dev/20100000.stm
> +root@genericarmv8:~# ls -l /dev/stm0
> +crw-------    1 root     root       10,  61 Jan  3 18:11 /dev/stm0
>  root@genericarmv8:~#
>
>  Details on how to use the generic STM API can be found here [2].
> --
> 2.7.4
>