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

[Sai Prakash Ranjan]

Hi,

On 2020-04-23 01:19, Doug Anderson wrote:
> Hi,
>
> On Tue, Mar 31, 2020 at 12:53 AM Sai Prakash Ranjan
> <saiprakash.ranjan@xxxxxxxxxxxxxx> wrote:
> > 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.
>
> Any update on the status here?  If I'm reading the conversation above,
> Robin said: "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".  Did I understand that
> properly?  If so, it seems like it's fully expected to see this
> message on every reboot and it doesn't necessarily signify anything
> bad.

Understanding is the same, waiting for Will and Robin to check if its OK
to make the message more friendly.

-Sai
--
QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a 
member
of Code Aurora Forum, hosted by The Linux Foundation