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

From: Robin Murphy
Date: Wed Jun 03 2020 - 09:40:58 EST

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 ;)


ÂÂ arm_smmu_device_shutdown()
ÂÂÂ platform_drv_shutdown()
ÂÂÂÂ device_shutdown()
ÂÂÂÂÂ kernel_restart_prepare()
ÂÂÂÂÂÂ kernel_restart()