Messages in this thread | | | Date | Mon, 08 Jun 2020 19:37:43 +0530 | From | Sai Prakash Ranjan <> | Subject | Re: [PATCH 2/2] coresight: tmc: Add shutdown callback for TMC ETR/ETF |
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Hi Mathieu, Mike
On 2020-06-04 12:57, Sai Prakash Ranjan wrote: >
[...]
>> >> Robin has a point - user space is long gone at this time. As such the >> first >> question to ask is what kind of CS session was running at the time the >> system >> was shutting down. Was it a perf session of a sysfs session? >> >> I'm guessing it was a sysfs session because user space has been blown >> away a >> while back and part of that process should have killed all perf >> sessions. > > I was enabling trace via sysfs. > >> >> If I am correct then simply switching off the ETR HW in the shutdown() >> amba bus >> callback should be fine - otherwise Mike's approach is mandatory. >> There is >> also the exchange between Robin and Sai about removing the SMMU >> shutdown >> callback, but that thread is still incomplete. >> > > If Robin is hinting at removing SMMU shutdown callback, then I think > adding > all these shutdown callbacks to all clients of SMMU can be avoided. Git > blaming > the thing shows it was added to avoid some kexec memory corruption. >
I think I misread the cryptic hint from Robin and it is not right to remove SMMU shutdown callback. For more details on why that was a bad idea and would break kexec, please refer to [1].
As for the coresight, can I disable the ETR only in the tmc shutdown callback or are we still concerned about the userspace coming into picture?
[1] https://lore.kernel.org/patchwork/patch/1253131/
Thanks, Sai
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