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

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Message-ID: <20200913032559.GT3715@yoga>
Date:   Sat, 12 Sep 2020 22:25:59 -0500
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Will Deacon <will@...nel.org>, 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 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.

Thanks,
Bjorn

> Robin.
> 
> > Signed-off-by: Bjorn Andersson <bjorn.andersson@...aro.org>
> > ---
> > 
> > Changes since v2:
> > - New patch/interface
> > 
> >   drivers/iommu/arm/arm-smmu/arm-smmu.c | 11 ++++++-----
> >   drivers/iommu/arm/arm-smmu/arm-smmu.h |  6 ++++++
> >   2 files changed, 12 insertions(+), 5 deletions(-)
> > 
> > diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu.c b/drivers/iommu/arm/arm-smmu/arm-smmu.c
> > index eb5c6ca5c138..4c4d302cd747 100644
> > --- a/drivers/iommu/arm/arm-smmu/arm-smmu.c
> > +++ b/drivers/iommu/arm/arm-smmu/arm-smmu.c
> > @@ -85,11 +85,6 @@ static inline void arm_smmu_rpm_put(struct arm_smmu_device *smmu)
> >   		pm_runtime_put_autosuspend(smmu->dev);
> >   }
> > -static struct arm_smmu_domain *to_smmu_domain(struct iommu_domain *dom)
> > -{
> > -	return container_of(dom, struct arm_smmu_domain, domain);
> > -}
> > -
> >   static struct platform_driver arm_smmu_driver;
> >   static struct iommu_ops arm_smmu_ops;
> > @@ -2188,6 +2183,12 @@ static int arm_smmu_device_probe(struct platform_device *pdev)
> >   	if (err)
> >   		return err;
> > +	if (smmu->impl->inherit_mappings) {
> > +		err = smmu->impl->inherit_mappings(smmu);
> > +		if (err)
> > +			return err;
> > +	}
> > +
> >   	if (smmu->version == ARM_SMMU_V2) {
> >   		if (smmu->num_context_banks > smmu->num_context_irqs) {
> >   			dev_err(dev,
> > diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu.h b/drivers/iommu/arm/arm-smmu/arm-smmu.h
> > index 235d9a3a6ab6..f58164976e74 100644
> > --- a/drivers/iommu/arm/arm-smmu/arm-smmu.h
> > +++ b/drivers/iommu/arm/arm-smmu/arm-smmu.h
> > @@ -378,6 +378,11 @@ struct arm_smmu_domain {
> >   	struct iommu_domain		domain;
> >   };
> > +static inline struct arm_smmu_domain *to_smmu_domain(struct iommu_domain *dom)
> > +{
> > +	return container_of(dom, struct arm_smmu_domain, domain);
> > +}
> > +
> >   struct arm_smmu_master_cfg {
> >   	struct arm_smmu_device		*smmu;
> >   	s16				smendx[];
> > @@ -442,6 +447,7 @@ struct arm_smmu_impl {
> >   	int (*alloc_context_bank)(struct arm_smmu_domain *smmu_domain,
> >   				  struct arm_smmu_device *smmu,
> >   				  struct device *dev, int start);
> > +	int (*inherit_mappings)(struct arm_smmu_device *smmu);
> >   };
> >   #define INVALID_SMENDX			-1
> >