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

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Message-ID: <6c0f45488f8a44bf860759e00fcabd09@codeaurora.org>
Date:   Tue, 07 Apr 2020 15:16:35 +0530
From:   Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
To:     Mike Leach <mike.leach@...aro.org>
Cc:     Mathieu Poirier <mathieu.poirier@...aro.org>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Leo Yan <leo.yan@...aro.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Stephen Boyd <swboyd@...omium.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org
Subject: Re: [RFC PATCH] coresight: dynamic-replicator: Fix handling of
 multiple connections

Hi Mike,

Thanks for taking a look.

On 2020-04-06 16:25, Mike Leach wrote:
> Hi,
> 
> The programmable replicator hardware by design enables trace through
> both ports on reset. (see 1, section 4.4, 9.11)  The replicator driver
> overrides this functionality to disable output, until the Coresight
> infrastructure chooses a path from source to sink.
> Now given that the hardware design is such that we must be able to
> allow trace to be sent to both ports, a generic patch to prevent this
> does not seem appropriate here.
> 
> I think this needs further investigation - to determine why this
> appears to be failing in this particular instance.
> 

Yes, this probably needs further investigation, but CPU hardlock stack
trace doesnt help much. I could always trigger this hard lockup without
this patch on SC7180 SoC and this is only seen when ETR is used as the 
sink.

The only difference I could see between non working case (on SC7180 [1]) 
and
the working case (on SDM845 [2]) is the path from source to sink.

SC7180 source to sink path(Not working):
----------------------------------------

       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


SDM845 source to sink path(Working):
------------------------------------

       etm0_out
          |
    apss_funnel_in0
          |
  apss_merge_funnel_in
          |
     funnel2_in5
	 |
   merge_funnel_in2
          |
       etf_in
	 |
   replicator_in
	 |
        etr_in


[1] - https://lore.kernel.org/patchwork/patch/1212946/
[2] - 
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm64/boot/dts/qcom/sdm845.dtsi?h=v5.6#n1910


Thanks,
Sai

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