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

[Sai Prakash Ranjan]

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

--
QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a 
member
of Code Aurora Forum, hosted by The Linux Foundation