On 08/06/2020 06:39 PM, Robin Murphy wrote:

On 2020-08-06 18:25, Robin Murphy wrote:

quoted

On 2020-08-06 17:33, Suzuki K Poulose wrote:

quoted

On 08/05/2020 05:29 PM, Suzuki K Poulose wrote:

quoted

On 08/05/2020 03:54 AM, Tingwei Zhang wrote:

quoted

Enhance coresight developer's efficiency to debug coresight drivers.
- Kconfig becomes a tristate, to allow =m
- append -core to source file name to allow module to
   be called coresight by the Makefile
- modules can have only one init/exit, so we add the etm_perf
   register/unregister function calls to the core init/exit
   functions.
- add a MODULE_DEVICE_TABLE for autoloading on boot
---
  drivers/hwtracing/coresight/Kconfig           |  5 ++-
  drivers/hwtracing/coresight/Makefile          |  5 ++-
  .../{coresight.c => coresight-core.c}         | 42 
++++++++++++++-----
  .../hwtracing/coresight/coresight-etm-perf.c  |  8 +++-
  .../hwtracing/coresight/coresight-etm-perf.h  |  3 ++
  5 files changed, 48 insertions(+), 15 deletions(-)
  rename drivers/hwtracing/coresight/{coresight.c => 
coresight-core.c} (98%)

Personally, I would like to rename this to core.c dropping the
"coresight-" prefix here (now that we have to do a rename). And we
should do that ideally for all the other files (but not proposing
it to be part of this series, and could be something that we could
pursue if everyone agrees to it).

We are inside the coresight directory anyways and having a prefix
doesn't help with anything.

The patch as such looks good to me.

Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>

On a second look, I believe for the sake of completion, we
should set the "owner" of the etm, now that we are a module.
The question is, which one should that be. It could be the
"coresight" or the "coresight-etm{3,4}x".

I believe the "coresight" is the better choice.

If you mean pmu->owner, you shouldn't really have much of a choice - it

...by which I meant pmu->module, obviously. Oops :)

Anyway, that should certainly be set not just for completeness but for 
correctness, since there do exist users who are adventurous enough to 
try unloading modules while perf is running.

Right. It should be the coresight module, as it holds the PMU code
and THIS_MODULE is sufficient.

Robin.

quoted

should be the module containing the actual PMU callbacks, such that 
they can't suddenly disappear while the PMU is in use. Allowing perf 
to take a reference to some other module and not actually protect 
itself would not be good. It should be pretty rare that the correct 
owner is anything other than THIS_MODULE ;)

Hopefully the dependencies are such that the core module automatically 
holds its own reference to the individual ETM driver module(s) by the 
time it registers the PMU.

This is taken care of by holding module reference whenever we prepare
a perf session.

Suzuki

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