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

Sai Prakash Ranjan
2020-03-27T15:10:11Z

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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