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

[Sai Prakash Ranjan]

Hi Will,

On 2020-03-31 13:14, Will Deacon wrote:
> On Tue, Mar 31, 2020 at 01:06:11PM +0530, Sai Prakash Ranjan wrote:
> > On 2020-03-30 23:54, Doug Anderson wrote:
> > > On Sat, Mar 28, 2020 at 12:35 AM Sai Prakash Ranjan
> > > <saiprakash.ranjan@xxxxxxxxxxxxxx> wrote:
> > > >
> > > > > Of course the fact that in practice we'll *always* see the warning
> > > > > because there's no way to tear down the default DMA domains, and even
> > > > > if all devices *have* been nicely quiesced there's no way to tell, is
> > > > > certainly less than ideal. Like I say, it's not entirely clear-cut
> > > > > either way...
> > > > >
> > > >
> > > > Thanks for these examples, good to know these scenarios in case we
> > > > come
> > > > across these.
> > > > However, if we see these error/warning messages appear everytime then
> > > > what will be
> > > > the credibility of these messages? We will just ignore these messages
> > > > when
> > > > these issues you mention actually appears because we see them
> > > > everytime
> > > > on
> > > > reboot or shutdown.
> > >
> > > I would agree that if these messages are expected to be seen every
> > > time, there's no way to fix them, and they're not indicative of any
> > > problem then something should be done.  Seeing something printed at
> > > "dev_error" level with an exclamation point (!) at the end makes me
> > > feel like this is something that needs immediate action on my part.
> > >
> > > If we really can't do better but feel that the messages need to be
> > > there, at least make them dev_info and less scary like:
> > >
> > >   arm-smmu 15000000.iommu: turning off; DMA should be quiesced before
> > > now
> > >
> > > ...that would still give you a hint in the logs that if you saw a DMA
> > > transaction after the message that it was a bug but also wouldn't
> > > sound scary to someone who wasn't seeing any other problems.
> > >
> >
> > We can do this if Robin is OK?
>
> It would be nice if you could figure out which domains are still live 
> when
> the SMMU is being shut down in your case and verify that it *is* infact
> benign before we start making the message more friendly. As Robin said
> earlier, rogue DMA is a real nightmare to debug.

I could see this error message for all the clients of apps_smmu.
I checked manually enabling bypass and removing iommus dt property
for each client of apps_smmu.

Thanks,
Sai

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