linux-kernel - Re: [PATCH 2/2] coresight: tmc: Add shutdown callback for TMC ETR/ETF

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Message-ID: <7fe5762b5cb8f87e988232922d06c55d@codeaurora.org>
Date:   Wed, 03 Jun 2020 17:56:21 +0530
From:   Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Mathieu Poirier <mathieu.poirier@...aro.org>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Mike Leach <mike.leach@...aro.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, coresight@...ts.linaro.org,
        Stephen Boyd <swboyd@...omium.org>
Subject: Re: [PATCH 2/2] coresight: tmc: Add shutdown callback for TMC ETR/ETF

Hi Robin,

On 2020-06-03 17:51, Robin Murphy wrote:
> On 2020-06-03 13:00, Sai Prakash Ranjan wrote:
>> Hi Robin, Mathieu
>> 
>> On 2020-06-03 17:07, Robin Murphy wrote:
>>> On 2020-06-01 22:28, Mathieu Poirier wrote:
>>>> That being said I'm sure that dependencies on an IOMMU isn't a 
>>>> problem confined
>>>> to coresight. I am adding Robin Murphy, who added this commit [1], 
>>>> to the thread
>>>> in the hope that he can provide guidance on the right way to do 
>>>> this.
>>> 
>>> Right, it's not specific to CoreSight, and it's not even specific to
>>> IOMMUs really. In short, blame kexec ;)
>>> 
>> 
>> Yes it is not specific to coresight, we are targeting this for all
>> consumers/clients of SMMU(atleast on SC7180 SoC). We have display 
>> throwing
>> NoC/interconnect errors[1] during reboot after SMMU is disabled.
>> This is also not specific to kexec either as you explained here [2] 
>> about
>> a case with display which is exacly what is happening in our system 
>> [1].
> 
> Sure, but those instances are begging the question of why the SMMU is
> disabled at reboot in the first place ;)
> 

That is what happens in SMMU shutdown callback right? It is the 
reboot/shutdown
flow.

    arm_smmu_device_shutdown()
     platform_drv_shutdown()
      device_shutdown()
       kernel_restart_prepare()
        kernel_restart()

Thanks,
Sai

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