[PATCH v3 09/10] iommu/arm-smmu: Get associated RMR info and install bypass SMR

[Robin Murphy]

On 2021-05-06 16:17, Steven Price wrote:
> On 20/04/2021 09:27, Shameer Kolothum wrote:
>> From: Jon Nettleton <jon at solid-run.com>
>>
>> Check if there is any RMR info associated with the devices behind
>> the SMMU and if any, install bypass SMRs for them. This is to
>> keep any ongoing traffic associated with these devices alive
>> when we enable/reset SMMU during probe().
>>
>> Signed-off-by: Jon Nettleton <jon at solid-run.com>
>> Signed-off-by: Shameer Kolothum <shameerali.kolothum.thodi at huawei.com>
>> ---
>>   drivers/iommu/arm/arm-smmu/arm-smmu.c | 42 +++++++++++++++++++++++++++
>>   drivers/iommu/arm/arm-smmu/arm-smmu.h |  2 ++
>>   2 files changed, 44 insertions(+)
>>
>> diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu.c 
>> b/drivers/iommu/arm/arm-smmu/arm-smmu.c
>> index d8c6bfde6a61..4d2f91626d87 100644
>> --- a/drivers/iommu/arm/arm-smmu/arm-smmu.c
>> +++ b/drivers/iommu/arm/arm-smmu/arm-smmu.c
>> @@ -2102,6 +2102,43 @@ err_reset_platform_ops: __maybe_unused;
>>       return err;
>>   }
>> +static void arm_smmu_rmr_install_bypass_smr(struct arm_smmu_device 
>> *smmu)
>> +{
>> +    struct iommu_rmr *e;
>> +    int i, cnt = 0;
>> +    u32 smr;
>> +
>> +    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))
>> +            continue;
>> +
>> +        list_for_each_entry(e, &smmu->rmr_list, list) {
>> +            if (FIELD_GET(ARM_SMMU_SMR_ID, smr) != e->sid)
>> +                continue;
>> +
>> +            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;
>> +
>> +            smmu->s2crs[i].type = S2CR_TYPE_BYPASS;
>> +            smmu->s2crs[i].privcfg = S2CR_PRIVCFG_DEFAULT;
>> +            smmu->s2crs[i].cbndx = 0xff;
>> +
>> +            cnt++;
>> +        }
>> +    }
> 
> If I understand this correctly - this is looking at the current
> (hardware) configuration of the SMMU and attempting to preserve any
> bypass SMRs. However from what I can tell it suffers from the following
> two problems:
> 
>   (a) Only the ID of the SMR is being checked, not the MASK. So if the
> firmware has setup an SMR matching a number of streams this will break.
> 
>   (b) The SMMU might not be enabled at all (CLIENTPD==1) or bypass
> enabled for unmatched streams (USFCFG==0).

Yes, trying to infer anything from the current SMMU hardware state is 
bogus - consider what you might find left over after a kexec, for 
instance. The *only* way to detect the presence and applicability of 
RMRs is to look at the actual RMR nodes in the IORT.

Ignore what we let the Qualcomm ACPI bootloader hack do - that whole 
implementation is "special".

Robin.

> Certainly in my test setup case (b) applies and so this doesn't work.
> Perhaps something like the below would work better? (It works in the
> case of the SMMU not enabled - I've not tested case (a)).
> 
> Steve
> 
> ----8<----
> static void arm_smmu_rmr_install_bypass_smr(struct arm_smmu_device *smmu)
> {
>      struct iommu_rmr *e;
>      int i, cnt = 0;
>      u32 smr;
>      u32 reg;
> 
>      reg = arm_smmu_gr0_read(smmu, ARM_SMMU_GR0_sCR0);
> 
>      if ((reg & ARM_SMMU_sCR0_USFCFG) && !(reg & ARM_SMMU_sCR0_CLIENTPD)) {
>          /*
>           * SMMU is already enabled and disallowing bypass, so preserve
>           * the existing SMRs
>           */
>          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))
>                  continue;
>              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;
>          }
>      }
> 
>      list_for_each_entry(e, &smmu->rmr_list, list) {
>          u32 sid = e->sid;
> 
>          i = arm_smmu_find_sme(smmu, sid, ~0);
>          if (i < 0)
>              continue;
>          if (smmu->s2crs[i].count == 0) {
>              smmu->smrs[i].id = sid;
>              smmu->smrs[i].mask = ~0;
>              smmu->smrs[i].valid = true;
>          }
>          smmu->s2crs[i].count++;
>          smmu->s2crs[i].type = S2CR_TYPE_BYPASS;
>          smmu->s2crs[i].privcfg = S2CR_PRIVCFG_DEFAULT;
>          smmu->s2crs[i].cbndx = 0xff;
> 
>          cnt++;
>      }
> 
>      if ((reg & ARM_SMMU_sCR0_USFCFG) && !(reg & ARM_SMMU_sCR0_CLIENTPD)) {
>          /* Remove the valid bit for unused SMRs */
>          for (i = 0; i < smmu->num_mapping_groups; i++) {
>              if (smmu->s2crs[i].count == 0)
>                  smmu->smrs[i].valid = false;
>          }
>      }
> 
>      dev_notice(smmu->dev, "\tpreserved %d boot mapping%s\n", cnt,
>             cnt == 1 ? "" : "s");
> }