Subject: Re: [PATCH 5/5] iommu/arm-smmu: Setup identity domain for boot mappings

From: Bjorn Andersson <[email-masked]>
Date: Thu, 9 Jul 2020 12:57:27 -0700

On Thu 09 Jul 08:50 PDT 2020, Laurentiu Tudor wrote:

> 
> 
> On 7/9/2020 8:01 AM, Bjorn Andersson wrote:
> > With many Qualcomm platforms not having functional S2CR BYPASS a
> > temporary IOMMU domain, without translation, needs to be allocated in
> > order to allow these memory transactions.
> > 
> > Unfortunately the boot loader uses the first few context banks, so
> > rather than overwriting a active bank the last context bank is used and
> > streams are diverted here during initialization.
> > 
> > This also performs the readback of SMR registers for the Qualcomm
> > platform, to trigger the mechanism.
> > 
> > This is based on prior work by Thierry Reding and Laurentiu Tudor.
> > 
> > Signed-off-by: Bjorn Andersson <[email-masked]>
> > ---
> >  drivers/iommu/arm-smmu-qcom.c | 11 +++++
> >  drivers/iommu/arm-smmu.c      | 80 +++++++++++++++++++++++++++++++++--
> >  drivers/iommu/arm-smmu.h      |  3 ++
> >  3 files changed, 90 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/iommu/arm-smmu-qcom.c b/drivers/iommu/arm-smmu-qcom.c
> > index 86b1917459a4..397df27c1d69 100644
> > --- a/drivers/iommu/arm-smmu-qcom.c
> > +++ b/drivers/iommu/arm-smmu-qcom.c
> > @@ -26,6 +26,7 @@ static const struct of_device_id qcom_smmu_client_of_match[] = {
> >  static int qcom_smmu_cfg_probe(struct arm_smmu_device *smmu)
> >  {
> >  	unsigned int last_s2cr = ARM_SMMU_GR0_S2CR(smmu->num_mapping_groups - 1);
> > +	u32 smr;
> >  	u32 reg;
> >  	int i;
> >  
> > @@ -56,6 +57,16 @@ static int qcom_smmu_cfg_probe(struct arm_smmu_device *smmu)
> >  		}
> >  	}
> >  
> > +	for (i = 0; i < smmu->num_mapping_groups; i++) {
> > +		smr = arm_smmu_gr0_read(smmu, ARM_SMMU_GR0_SMR(i));
> > +
> > +		if (FIELD_GET(ARM_SMMU_SMR_VALID, smr)) {
> > +			smmu->smrs[i].id = FIELD_GET(ARM_SMMU_SMR_ID, smr);
> > +			smmu->smrs[i].mask = FIELD_GET(ARM_SMMU_SMR_MASK, smr);
> > +			smmu->smrs[i].valid = true;
> > +		}
> > +	}
> > +
> >  	return 0;
> >  }
> >  
> > diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
> > index e2d6c0aaf1ea..a7cb27c1a49e 100644
> > --- a/drivers/iommu/arm-smmu.c
> > +++ b/drivers/iommu/arm-smmu.c
> > @@ -652,7 +652,8 @@ static void arm_smmu_write_context_bank(struct arm_smmu_device *smmu, int idx)
> >  }
> >  
> >  static int arm_smmu_init_domain_context(struct iommu_domain *domain,
> > -					struct arm_smmu_device *smmu)
> > +					struct arm_smmu_device *smmu,
> > +					bool boot_domain)
> >  {
> >  	int irq, start, ret = 0;
> >  	unsigned long ias, oas;
> > @@ -770,6 +771,15 @@ static int arm_smmu_init_domain_context(struct iommu_domain *domain,
> >  		ret = -EINVAL;
> >  		goto out_unlock;
> >  	}
> > +
> > +	/*
> > +	 * Use the last context bank for identity mappings during boot, to
> > +	 * avoid overwriting in-use bank configuration while we're setting up
> > +	 * the new mappings.
> > +	 */
> > +	if (boot_domain)
> > +		start = smmu->num_context_banks - 1;
> > +
> >  	ret = __arm_smmu_alloc_bitmap(smmu->context_map, start,
> >  				      smmu->num_context_banks);
> >  	if (ret < 0)
> > @@ -1149,7 +1159,10 @@ static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev)
> >  	struct iommu_fwspec *fwspec = dev_iommu_fwspec_get(dev);
> >  	struct arm_smmu_master_cfg *cfg;
> >  	struct arm_smmu_device *smmu;
> > +	bool free_identity_domain = false;
> > +	int idx;
> >  	int ret;
> > +	int i;
> >  
> >  	if (!fwspec || fwspec->ops != &arm_smmu_ops) {
> >  		dev_err(dev, "cannot attach to SMMU, is it on the same bus?\n");
> > @@ -1174,7 +1187,7 @@ static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev)
> >  		return ret;
> >  
> >  	/* Ensure that the domain is finalised */
> > -	ret = arm_smmu_init_domain_context(domain, smmu);
> > +	ret = arm_smmu_init_domain_context(domain, smmu, false);
> >  	if (ret < 0)
> >  		goto rpm_put;
> >  
> > @@ -1190,9 +1203,34 @@ static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev)
> >  		goto rpm_put;
> >  	}
> >  
> > +	/* Decrement use counter for any references to the identity domain */
> > +	mutex_lock(&smmu->stream_map_mutex);
> > +	if (smmu->identity) {
> > +		struct arm_smmu_domain *identity = to_smmu_domain(smmu->identity);
> > +
> > +		for_each_cfg_sme(cfg, fwspec, i, idx) {
> > +			dev_err(smmu->dev, "%s() %#x\n", __func__, smmu->smrs[idx].id);
> 
> Debug leftovers?
> 

Indeed.

> Apart from that I plan to give this a go on some NXP chips. Will keep
> you updated.
> 

Thanks, I'm expecting that all you need is the first patch in the series
and some impl specific cfg_probe that sets up (or read back) the
relevant SMRs and mark them valid.

Regards,
Bjorn

> Thanks a lot Bjorn.

> ---
> Best Regards, Laurentiu

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