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

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Date:   Tue, 31 Mar 2020 13:06:11 +0530
From:   Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
To:     Doug Anderson <dianders@...omium.org>
Cc:     Robin Murphy <robin.murphy@....com>, Will Deacon <will@...nel.org>,
        Joerg Roedel <joro@...tes.org>,
        "list@....net:IOMMU DRIVERS , Joerg Roedel <joro@...tes.org>," 
        <iommu@...ts.linux-foundation.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] iommu/arm-smmu: Demote error messages to debug in
 shutdown callback

Hi,

On 2020-03-30 23:54, Doug Anderson wrote:
> Hi,
> 
> On Sat, Mar 28, 2020 at 12:35 AM Sai Prakash Ranjan
> <saiprakash.ranjan@...eaurora.org> 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?

-Sai

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