Re: [PATCH 3/6] iommu/arm-smmu: add support for iova_to_phys through ATS1PR

Will Deacon
2014-08-19T12:44:32Z

On Wed, Aug 13, 2014 at 01:51:36AM +0100, Mitchel Humpherys wrote:
> Currently, we provide the iommu_ops.iova_to_phys service by doing a
> table walk in software to translate IO virtual addresses to physical
> addresses. On SMMUs that support it, it can be useful to ask the SMMU
> itself to do the translation. This can be used to warm the TLBs for an
> SMMU. It can also be useful for testing and hardware validation.

I'm not really sold on the usefulness of this feature. If you want hardware
validation features, I'd rather do something through debugfs, but your
use-case for warming the TLBs is intriguing. Do you have an example use-case
with performance figures?

> Since the address translation registers are optional on SMMUv2, only
> enable hardware translations when using SMMUv1 or when SMMU_IDR0.S1TS=1
> and SMMU_IDR0.ATOSNS=0, as described in the ARM SMMU v1-v2 spec.

[...]

> +static phys_addr_t arm_smmu_iova_to_phys_hard(struct iommu_domain *domain,
> + dma_addr_t iova)
> +{
> + struct arm_smmu_domain *smmu_domain = domain->priv;
> + struct arm_smmu_device *smmu = smmu_domain->smmu;
> + struct arm_smmu_cfg *cfg = &smmu_domain->cfg;
> + struct device *dev = smmu->dev;
> + void __iomem *cb_base;
> + int count = 0;
> + u64 phys;
> +
> + arm_smmu_enable_clocks(smmu);
> +
> + cb_base = ARM_SMMU_CB_BASE(smmu) + ARM_SMMU_CB(smmu, cfg->cbndx);
> +
> + if (smmu->version == 1) {
> + u32 reg = iova & 0xFFFFF000;
> + writel_relaxed(reg, cb_base + ARM_SMMU_CB_ATS1PR_LO);
> + } else {
> + u64 reg = iova & 0xfffffffffffff000;
> + writeq_relaxed(reg, cb_base + ARM_SMMU_CB_ATS1PR_LO);

We don't have writeq for arch/arm/.

> + }
> +
> + mb();

Why?

> + while (readl_relaxed(cb_base + ARM_SMMU_CB_ATSR) & ATSR_ACTIVE) {
> + if (++count == ATSR_LOOP_TIMEOUT) {
> + dev_err(dev,
> + "iova to phys timed out on 0x%pa for %s. Falling back to software table walk.\n",
> + &iova, dev_name(dev));
> + arm_smmu_disable_clocks(smmu);
> + return arm_smmu_iova_to_phys_soft(domain, iova);
> + }
> + cpu_relax();
> + }

Do you know what happened to Olav's patches to make this sort of code
generic?

> @@ -2005,6 +2073,11 @@ int arm_smmu_device_cfg_probe(struct arm_smmu_device *smmu)
> return -ENODEV;
> }
>
> + if (smmu->version == 1 || (!(id & ID0_ATOSNS) && (id & ID0_S1TS))) {

Are you sure about this? The v2 spec says that is ATOSNS is clear then S1TS
is also clear.

Will