linux-kernel - Re: [PATCH v3 6/8] iommu/arm-smmu: Add impl hook for inherit boot mappings

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Message-ID: <20200924155507.GE40811@yoga>
Date:   Thu, 24 Sep 2020 10:55:07 -0500
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Will Deacon <will@...nel.org>
Cc:     Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>,
        Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>,
        Jordan Crouse <jcrouse@...eaurora.org>,
        Rob Clark <robdclark@...omium.org>,
        Sibi Sankar <sibis@...eaurora.org>,
        linux-arm-kernel@...ts.infradead.org,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v3 6/8] iommu/arm-smmu: Add impl hook for inherit boot
 mappings

On Mon 21 Sep 16:08 CDT 2020, Will Deacon wrote:

> On Sat, Sep 12, 2020 at 10:25:59PM -0500, Bjorn Andersson wrote:
> > On Fri 11 Sep 12:13 CDT 2020, Robin Murphy wrote:
> > > On 2020-09-04 16:55, Bjorn Andersson wrote:
> > > > Add a new operation to allow platform implementations to inherit any
> > > > stream mappings from the boot loader.
> > > 
> > > Is there a reason we need an explicit step for this? The aim of the
> > > cfg_probe hook is that the SMMU software state should all be set up by then,
> > > and you can mess about with it however you like before arm_smmu_reset()
> > > actually commits anything to hardware. I would have thought you could
> > > permanently steal a context bank, configure it as your bypass hole, read out
> > > the previous SME configuration and tweak smmu->smrs and smmu->s2crs
> > > appropriately all together "invisibly" at that point.
> > 
> > I did this because as of 6a79a5a3842b ("iommu/arm-smmu: Call
> > configuration impl hook before consuming features") we no longer have
> > setup pgsize_bitmap as we hit cfg_probe, which means that I need to
> > replicate this logic to set up the iommu_domain.
> > 
> > If I avoid setting up an iommu_domain for the identity context, as you
> > request in patch 8, this shouldn't be needed anymore.
> > 
> > > If that can't work, I'm very curious as to what I've overlooked.
> > > 
> > 
> > I believe that will work, I will rework the patches and try it out.
> 
> Did you get a chance to rework this?
> 

Unfortunately not, I hope to get to this shortly.

Thanks,
Bjorn