Re: [PATCH] iommu/arm-smmu: Demote error messages to debug in shutdown callback

[Sai Prakash Ranjan]

Hi Rob,

On 2020-03-27 21:47, Rob Clark wrote:
> On Fri, Mar 27, 2020 at 8:10 AM Sai Prakash Ranjan
> <saiprakash.ranjan@xxxxxxxxxxxxxx> wrote:
> > Hi Robin,
> >
> > Thanks for taking a look at this.
> >
> > On 2020-03-27 19:42, Robin Murphy wrote:
> > > On 2020-03-27 1:28 pm, Sai Prakash Ranjan wrote:
> > >> Currently on reboot/shutdown, the following messages are
> > >> displayed on the console as error messages before the
> > >> system reboots/shutdown.
> > >>
> > >> On SC7180:
> > >>
> > >>    arm-smmu 15000000.iommu: removing device with active domains!
> > >>    arm-smmu 5040000.iommu: removing device with active domains!
> > >>
> > >> Demote the log level to debug since it does not offer much
> > >> help in identifying/fixing any issue as the system is anyways
> > >> going down and reduce spamming the kernel log.
> > >
> > > I've gone back and forth on this pretty much ever since we added the
> > > shutdown hook - on the other hand, if any devices *are* still running
> > > in those domains at this point, then once we turn off the SMMU and let
> > > those IOVAs go out on the bus as physical addresses, all manner of
> > > weirdness may ensue. Thus there is an argument for *some* indication
> > > that this may happen, although IMO it could be downgraded to at least
> > > dev_warn().
> > >
> >
> > Any pointers to the weirdness here after SMMU is turned off?
> > Because if we look at the call sites, device_shutdown is called
> > from kernel_restart_prepare or kernel_shutdown_prepare which would
> > mean system is going down anyways, so do we really care about these
> > error messages or warnings from SMMU?
> >
> >   arm_smmu_device_shutdown
> >    platform_drv_shutdown
> >     device_shutdown
> >      kernel_restart_prepare
> >       kernel_restart
>
> I'd guess that drm/msm is not detaching all of it's UNMANAGED domains
> in shutdown.  Although *presumably* the device_link stuff would
> prevent the SMMU from shutting down while gpu/display is still active?
>  If not I think we have bigger problems.

Where is the shutdown callback in drm/msm? I don't see any...

Thanks,
Sai

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