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

[Doug Anderson <dianders@chromium.org>]

Hi,

On Sat, Mar 28, 2020 at 12:35 AM Sai Prakash Ranjan
<saiprakash.ranjan@codeaurora.org> 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.

-Doug