Re: [PATCH v2 4/4] iommu/arm-smmu: Add support to handle Qcom's TLBI serialization errata

[Vivek Gautam]

Hi Robin,

On Tue, Sep 25, 2018 at 6:01 PM Robin Murphy <robin.murphy@xxxxxxx> wrote:
>
> On 10/09/18 07:25, Vivek Gautam wrote:
> > Qcom's implementation of arm,mmu-500 require to serialize all
> > TLB invalidations for context banks.
>
> What does "serailize all TLB invalidations" actually mean, because it's
> not entirely clear from context, and furthermore this patch appears to
> behave subtly differently to the downstream code so I'm really
> struggling to figure out whether it's actually doing what it's intended
> to do.

Adding Pratik Patel from downstream team.

Thanks for taking a look at this.
We want to space out the TLB invalidation and then the workaround
to toggle wait-safe logic would let the safe checks in HW work and
only allow invalidation to occur when device is expected to not
run into underruns.

> > In case the TLB invalidation requests don't go through the first
> > time, there's a way to disable/enable the wait for safe logic.
> > Disabling this logic expadites the TLBIs.
> >
> > Different bootloaders with their access control policies allow this
> > register access differntly. With one, we should be able to directly
> > make qcom-scm call to do io read/write, while with other we should
> > use the specific SCM command to send request to do the complete
> > register configuration.
> > A separate device tree flag for arm-smmu will allow to identify
> > which firmware configuration of the two mentioned above we use.
> >
> > Signed-off-by: Vivek Gautam <vivek.gautam@xxxxxxxxxxxxxx>
> > ---
> >   drivers/iommu/arm-smmu-regs.h |   2 +
> >   drivers/iommu/arm-smmu.c      | 133 +++++++++++++++++++++++++++++++++++++++++-
> >   2 files changed, 133 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/iommu/arm-smmu-regs.h b/drivers/iommu/arm-smmu-regs.h
> > index a1226e4ab5f8..71662cae9806 100644
> > --- a/drivers/iommu/arm-smmu-regs.h
> > +++ b/drivers/iommu/arm-smmu-regs.h
> > @@ -177,6 +177,8 @@ enum arm_smmu_s2cr_privcfg {
> >   #define ARM_SMMU_CB_ATS1PR          0x800
> >   #define ARM_SMMU_CB_ATSR            0x8f0
> >
> > +#define ARM_SMMU_GID_QCOM_CUSTOM_CFG 0x300
> > +
> >   #define SCTLR_S1_ASIDPNE            (1 << 12)
> >   #define SCTLR_CFCFG                 (1 << 7)
> >   #define SCTLR_CFIE                  (1 << 6)
> > diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
> > index 411e5ac57c64..de9c4a5bf686 100644
> > --- a/drivers/iommu/arm-smmu.c
> > +++ b/drivers/iommu/arm-smmu.c
> > @@ -49,6 +49,7 @@
> >   #include <linux/pci.h>
> >   #include <linux/platform_device.h>
> >   #include <linux/pm_runtime.h>
> > +#include <linux/qcom_scm.h>
> >   #include <linux/slab.h>
> >   #include <linux/spinlock.h>
> >
> > @@ -181,7 +182,8 @@ struct arm_smmu_device {
> >   #define ARM_SMMU_FEAT_EXIDS         (1 << 12)
> >       u32                             features;
> >
> > -#define ARM_SMMU_OPT_SECURE_CFG_ACCESS (1 << 0)
> > +#define ARM_SMMU_OPT_SECURE_CFG_ACCESS        (1 << 0)
> > +#define ARM_SMMU_OPT_QCOM_FW_IMPL_ERRATA (1 << 1)
> >       u32                             options;
> >       enum arm_smmu_arch_version      version;
> >       enum arm_smmu_implementation    model;
> > @@ -266,6 +268,7 @@ static bool using_legacy_binding, using_generic_binding;
> >
> >   static struct arm_smmu_option_prop arm_smmu_options[] = {
> >       { ARM_SMMU_OPT_SECURE_CFG_ACCESS, "calxeda,smmu-secure-config-access" },
> > +     { ARM_SMMU_OPT_QCOM_FW_IMPL_ERRATA, "qcom,smmu-500-fw-impl-errata" },
> >       { 0, NULL},
> >   };
> >
> > @@ -531,12 +534,134 @@ static void arm_smmu_tlb_inv_vmid_nosync(unsigned long iova, size_t size,
> >       writel_relaxed(smmu_domain->cfg.vmid, base + ARM_SMMU_GR0_TLBIVMID);
> >   }
> >
> > +#define CUSTOM_CFG_MDP_SAFE_ENABLE           BIT(15)
> > +#define CUSTOM_CFG_IFE1_SAFE_ENABLE          BIT(14)
> > +#define CUSTOM_CFG_IFE0_SAFE_ENABLE          BIT(13)
> > +
> > +static int __qsmmu500_wait_safe_toggle(struct arm_smmu_device *smmu, int en)
> > +{
> > +     int ret;
> > +     u32 val, gid_phys_base;
> > +     phys_addr_t reg;
> > +     struct vm_struct *vm;
> > +
> > +     /* We want physical address of SMMU, so the vm_area */
> > +     vm = find_vm_area(smmu->base);
> > +
> > +     /*
> > +      * GID (implementation defined address space) is located at
> > +      * SMMU_BASE + (2 Ã PAGESIZE).
> > +      */
> > +     gid_phys_base = vm->phys_addr + (2 << (smmu)->pgshift);
> > +     reg = gid_phys_base + ARM_SMMU_GID_QCOM_CUSTOM_CFG;
> > +
> > +     ret = qcom_scm_io_readl_atomic(reg, &val);
> > +     if (ret)
> > +             return ret;
> > +
> > +     if (en)
> > +             val |= CUSTOM_CFG_MDP_SAFE_ENABLE |
> > +                    CUSTOM_CFG_IFE0_SAFE_ENABLE |
> > +                    CUSTOM_CFG_IFE1_SAFE_ENABLE;
> > +     else
> > +             val &= ~(CUSTOM_CFG_MDP_SAFE_ENABLE |
> > +                      CUSTOM_CFG_IFE0_SAFE_ENABLE |
> > +                      CUSTOM_CFG_IFE1_SAFE_ENABLE);
> > +
> > +     ret = qcom_scm_io_writel_atomic(reg, val);
> > +
> > +     return ret;
> > +}
> > +
> > +static int qsmmu500_wait_safe_toggle(struct arm_smmu_device *smmu,
> > +                                  int en, bool is_fw_impl)
> > +{
> > +     if (is_fw_impl)
> > +             return qcom_scm_qsmmu500_wait_safe_toggle(en);
> > +     else
> > +             return __qsmmu500_wait_safe_toggle(smmu, en);
> > +}
> > +
> > +static void qcom_errata_tlb_sync(struct arm_smmu_domain *smmu_domain)
> > +{
> > +     struct arm_smmu_device *smmu = smmu_domain->smmu;
> > +     void __iomem *base = ARM_SMMU_CB(smmu, smmu_domain->cfg.cbndx);
> > +     bool is_fw_impl;
> > +     u32 val;
> > +
> > +     writel_relaxed(0, base + ARM_SMMU_CB_TLBSYNC);
> > +
> > +     if (!readl_poll_timeout_atomic(base + ARM_SMMU_CB_TLBSTATUS, val,
> > +                                    !(val & sTLBGSTATUS_GSACTIVE), 0, 100))
> > +             return;
> > +
> > +     is_fw_impl = smmu->options & ARM_SMMU_OPT_QCOM_FW_IMPL_ERRATA ?
> > +                     true : false;
> > +
> > +     /* SCM call here to disable the wait-for-safe logic. */
>
> I take it this is a global state, so it can't just be turned off for the
> relevant contexts and left that way?

Yes this is a global state disable/enable. But can we disable it for
the required context altogether forever, I will have to find it out.

>
> > +     if (WARN(qsmmu500_wait_safe_toggle(smmu, false, is_fw_impl),
> > +              "Failed to disable wait-safe logic, bad hw state\n"))
> > +             return;
> > +
> > +     if (!readl_poll_timeout_atomic(base + ARM_SMMU_CB_TLBSTATUS, val,
> > +                                    !(val & sTLBGSTATUS_GSACTIVE), 0, 10000))
> > +             return;
> > +
> > +     /* SCM call here to re-enable the wait-for-safe logic. */
> > +     WARN(qsmmu500_wait_safe_toggle(smmu, true, is_fw_impl),
> > +          "Failed to re-enable wait-safe logic, bad hw state\n");
> > +
> > +     dev_err_ratelimited(smmu->dev,
> > +                         "TLB sync timed out -- SMMU in bad state\n");
> > +}
> > +
> > +static void qcom_errata_tlb_sync_context(void *cookie)
> > +{
> > +     struct arm_smmu_domain *smmu_domain = cookie;
> > +     unsigned long flags;
> > +
> > +     spin_lock_irqsave(&smmu_domain->cb_lock, flags);
> > +     qcom_errata_tlb_sync(smmu_domain);
> > +     spin_unlock_irqrestore(&smmu_domain->cb_lock, flags);
> > +}
> > +
> > +static void qcom_errata_tlb_inv_context_s1(void *cookie)
> > +{
> > +     struct arm_smmu_domain *smmu_domain = cookie;
> > +     struct arm_smmu_cfg *cfg = &smmu_domain->cfg;
> > +     void __iomem *base = ARM_SMMU_CB(smmu_domain->smmu, cfg->cbndx);
> > +     unsigned long flags;
> > +
> > +     spin_lock_irqsave(&smmu_domain->cb_lock, flags);
> > +     writel_relaxed(cfg->asid, base + ARM_SMMU_CB_S1_TLBIASID);
> > +     qcom_errata_tlb_sync(cookie);
> > +     spin_unlock_irqrestore(&smmu_domain->cb_lock, flags);
> > +}
> > +
> > +static void qcom_errata_tlb_inv_range_nosync(unsigned long iova, size_t size,
> > +                                          size_t granule, bool leaf,
> > +                                          void *cookie)
> > +{
> > +     struct arm_smmu_domain *smmu_domain = cookie;
> > +     unsigned long flags;
> > +
> > +     spin_lock_irqsave(&smmu_domain->cb_lock, flags);
> > +     arm_smmu_tlb_inv_range_nosync(iova, size, granule, leaf, cookie);
> > +     spin_unlock_irqrestore(&smmu_domain->cb_lock, flags);
>
> I don't get what this locking is trying to achieve - the only thing it
> protects is one or more writes to TLBIVA{L}, which *must* surely be
> "serialised" by the interconnect anyway?
>

Okay, right. This callback is just a write to TLBIVA{L} registers, so this
should be good without any locking.
A subsequent .tlb_sync has the locking anyways.

> The downstream code doesn't appear to implement .tlb_add_flush at all,
> so something smells off.

Yes, the downstream pg-table driver never uses tlb_add_flush and
tlb_sync to do TLBIs.
Rather it relies on tlb_flush_all to flush the entire TLB after the
unmap is finished.
Moreover, in downstream a global remote spinlock is used to protect
the invalidation
requests owing to other entities besides kernel handling the TLB operations.

Assuming we don't want to do tlb_flush_all, we still want to serialize
the invalidation
requests, and then toggle the wait-safe logic too.
We would also not want the remote spinlock as we are invalidating based on ASIDs
in the kernel.

Regards
Vivek

>
> Robin.
>
> > +}
> > +
> >   static const struct iommu_gather_ops arm_smmu_s1_tlb_ops = {
> >       .tlb_flush_all  = arm_smmu_tlb_inv_context_s1,
> >       .tlb_add_flush  = arm_smmu_tlb_inv_range_nosync,
> >       .tlb_sync       = arm_smmu_tlb_sync_context,
> >   };
> >
> > +static const struct iommu_gather_ops qcom_errata_s1_tlb_ops = {
> > +     .tlb_flush_all  = qcom_errata_tlb_inv_context_s1,
> > +     .tlb_add_flush  = qcom_errata_tlb_inv_range_nosync,
> > +     .tlb_sync       = qcom_errata_tlb_sync_context,
> > +};
> > +
> >   static const struct iommu_gather_ops arm_smmu_s2_tlb_ops_v2 = {
> >       .tlb_flush_all  = arm_smmu_tlb_inv_context_s2,
> >       .tlb_add_flush  = arm_smmu_tlb_inv_range_nosync,
> > @@ -824,7 +949,11 @@ static int arm_smmu_init_domain_context(struct iommu_domain *domain,
> >                       ias = min(ias, 32UL);
> >                       oas = min(oas, 32UL);
> >               }
> > -             smmu_domain->tlb_ops = &arm_smmu_s1_tlb_ops;
> > +             if (of_device_is_compatible(smmu->dev->of_node,
> > +                                         "qcom,sdm845-smmu-500"))
> > +                     smmu_domain->tlb_ops = &qcom_errata_s1_tlb_ops;
> > +             else
> > +                     smmu_domain->tlb_ops = &arm_smmu_s1_tlb_ops;
> >               break;
> >       case ARM_SMMU_DOMAIN_NESTED:
> >               /*
> >
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