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

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Date:   Fri, 27 Mar 2020 09:17:03 -0700
From:   Rob Clark <robdclark@...il.com>
To:     Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
Cc:     Robin Murphy <robin.murphy@....com>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Douglas Anderson <dianders@...omium.org>,
        "list@....net:IOMMU DRIVERS <iommu@...ts.linux-foundation.org>, Joerg
        Roedel <joro@...tes.org>," <iommu@...ts.linux-foundation.org>,
        Will Deacon <will@...nel.org>
Subject: Re: [PATCH] iommu/arm-smmu: Demote error messages to debug in
 shutdown callback

On Fri, Mar 27, 2020 at 8:10 AM Sai Prakash Ranjan
<saiprakash.ranjan@...eaurora.org> 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.

I hadn't really noticed the error msgs before, not sure if that is
just because the screen is off by the time they happen or if they are
a new warning..

BR,
-R