Messages in this thread | | | Date | Tue, 09 Jun 2020 21:07:16 +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,
On 2020-06-09 20:57, Mathieu Poirier wrote: > On Mon, 8 Jun 2020 at 08:07, Sai Prakash Ranjan > <saiprakash.ranjan@codeaurora.org> wrote: >> >> 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? > > User space isn't a concern, especially after you've confirmed the > problem occured during an ongoing sysfs session. >
Will post v3 with comments addressed after 5.8-rc1 is out.
Thanks, Sai
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