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

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Date:   Fri, 27 Mar 2020 20:39:46 +0530
From:   Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Will Deacon <will@...nel.org>, Joerg Roedel <joro@...tes.org>,
        iommu@...ts.linux-foundation.org,
        Douglas Anderson <dianders@...omium.org>,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iommu/arm-smmu: Demote error messages to debug in
 shutdown callback

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


Thanks,
Sai

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