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

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Message-ID: <0148cf32b9770ad4b5b4f7baf4541a40@codeaurora.org>
Date:   Fri, 27 Mar 2020 23:48:31 +0530
From:   Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
To:     Rob Clark <robdclark@...il.com>
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 , 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

Hi Rob,

On 2020-03-27 21:47, Rob Clark wrote:
> 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.
> 

Where is the shutdown callback in drm/msm? I don't see any...

Thanks,
Sai

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