Re: [PATCH] coresight: dynamic-replicator: Fix handling of multiple connections

[Suzuki K Poulose]

On 04/27/2020 10:45 AM, Mike Leach wrote:
> HI,
>
> On Mon, 27 Apr 2020 at 10:15, Suzuki K Poulose <suzuki.poulose@xxxxxxx> wrote:
> > On 04/26/2020 03:37 PM, Sai Prakash Ranjan wrote:
> > > Since commit 30af4fb619e5 ("coresight: dynamic-replicator:
> > > Handle multiple connections"), we do not make sure that
> > > the other port is disabled when the dynamic replicator is
> > > enabled. This is seen to cause the CPU hardlockup atleast
> > > on SC7180 SoC with the following topology when enabling ETM
> > > with ETR as the sink via sysfs. Since there is no trace id
> > > logic in coresight yet to make use of multiple sinks in
> > > parallel for different trace sessions, disable the other
> > > port when one port is turned on.
> > >
> > >          etm0_out
> > >          |
> > >      apss_funnel_in0
> > >             |
> > >     apss_merge_funnel_in
> > >             |
> > >         funnel1_in4
> > >          |
> > >      merge_funnel_in1
> > >          |
> > >       swao_funnel_in
> > >             |
> > >           etf_in
> > >          |
> > >     swao_replicator_in
> > >             |
> > >      replicator_in
> > >          |
> > >           etr_in
> > >
> > >     Kernel panic - not syncing: Watchdog detected hard LOCKUP on cpu 0
> > >     CPU: 7 PID: 0 Comm: swapper/7 Tainted: G S  B             5.4.25 #100
> > >     Hardware name: Qualcomm Technologies, Inc. SC7180 IDP (DT)
> > >     Call trace:
> > >      dump_backtrace+0x0/0x188
> > >      show_stack+0x20/0x2c
> > >      dump_stack+0xdc/0x144
> > >      panic+0x168/0x370
> > >      arch_seccomp_spec_mitigate+0x0/0x14
> > >      watchdog_timer_fn+0x68/0x290
> > >      __hrtimer_run_queues+0x264/0x498
> > >      hrtimer_interrupt+0xf0/0x22c
> > >      arch_timer_handler_phys+0x40/0x50
> > >      handle_percpu_devid_irq+0x8c/0x158
> > >      __handle_domain_irq+0x84/0xc4
> > >      gic_handle_irq+0x100/0x1c4
> > >      el1_irq+0xbc/0x180
> > >      arch_cpu_idle+0x3c/0x5c
> > >      default_idle_call+0x1c/0x38
> > >      do_idle+0x100/0x280
> > >      cpu_startup_entry+0x24/0x28
> > >      secondary_start_kernel+0x15c/0x170
> > >     SMP: stopping secondary CPUs
> > >
> > > Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@xxxxxxxxxxxxxx>
> > > Tested-by: Stephen Boyd <swboyd@xxxxxxxxxxxx>


> > This is not sufficient. You must prevent another session trying to
> > enable the other port of the replicator as this could silently fail
> > the "on-going" session. Not ideal. Fail the attempt to enable a port
> > if the other port is active. You could track this in software and
> > fail early.
> >
> > Suzuki
>
> While I have no issue in principle with not enabling a path to a sink
> that is not in use - indeed in some cases attaching to unused sinks
> can cause back-pressure that slows throughput (cf TPIU) - I am
> concerned that this modification is masking an underlying issue with
> the platform in question.
>
> Should we decide to enable the diversion of different IDs to different
> sinks or allow different sessions go to different sinks, then this has
> potential to fail on the SC7180 SoC - and it will be difficult in
> future to associate a problem with this discussion.

Mike,

I think thats a good point.
Sai, please could we narrow down this to the real problem and may be
work around it for the "device" ? Do we know which sink is causing the
back pressure ? We could then push the "work around" to the replicator
it is connected to.

Suzuki