linux-kernel - Re: [RFC] iommu: arm-smmu: stall support

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Message-ID: <20170922090204.GJ8398@8bytes.org>
Date:   Fri, 22 Sep 2017 11:02:05 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     Rob Clark <robdclark@...il.com>
Cc:     "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Jordan Crouse <jcrouse@...eaurora.org>,
        Will Deacon <will.deacon@....com>,
        Robin Murphy <robin.murphy@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] iommu: arm-smmu: stall support

On Tue, Sep 19, 2017 at 10:23:43AM -0400, Rob Clark wrote:
> I would like to decide in the IRQ whether or not to queue work or not,
> because when we get a gpu fault, we tend to get 1000's of gpu faults
> all at once (and I really only need to handle the first one).  I
> suppose that could also be achieved by having a special return value
> from the fault handler to say "call me again from a wq"..
> 
> Note that in the drm driver I already have a suitable wq to queue the
> work, so it really doesn't buy me anything to have the iommu driver
> toss things off to a wq for me.  Might be a different situation for
> other drivers (but I guess mostly other drivers are using iommu API
> indirectly via dma-mapping?)

Okay, so since you are the only user for now, we don't need a
work-queue. But I still want the ->resume call-back to be hidden in the
iommu code and not be exposed to users.

We already have per-domain fault-handlers, so the best solution for now
is to call ->resume from report_iommu_fault() when the fault-handler
returns a special value.


Regards,

	Joerg