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

[Robin Murphy]

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/`

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 ;)

Robin.

>  ÂÂ arm_smmu_device_shutdown()
>  ÂÂÂ platform_drv_shutdown()
>  ÂÂÂÂ device_shutdown()
>  ÂÂÂÂÂ kernel_restart_prepare()
>  ÂÂÂÂÂÂ kernel_restart()
>
> Thanks,
> Sai