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

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Message-ID: <c3b17c472783faa6f153bccc157ad8c4@codeaurora.org>
Date:   Wed, 03 Jun 2020 19:21:04 +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 19:10, Robin Murphy wrote:
> On 2020-06-03 13:26, Sai Prakash Ranjan wrote:
>> 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.
> 
> Yes, that's where it happens, but my point is *why* it happens at all.
> 
> hint: `git log --grep=shutdown drivers/iommu/`
> 

Ah my change :)

> If we could assume the system is always about to be powered off or
> reset, we wouldn't need to do anything to the SMMU either ;)
> 

Are you hinting at removing SMMU shutdown callback altogether ;)

Thanks,
Sai

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