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

[Jon Nettleton <jon@solid-run.com>]

On Mon, May 10, 2021 at 10:40 AM Shameerali Kolothum Thodi
<shameerali.kolothum.thodi@huawei.com> wrote:
>
>
>
> > -----Original Message-----
> > From: Steven Price [mailto:steven.price@arm.com]
> > Sent: 06 May 2021 16:17
> > To: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>;
> > linux-arm-kernel@lists.infradead.org; linux-acpi@vger.kernel.org;
> > iommu@lists.linux-foundation.org
> > Cc: Linuxarm <linuxarm@huawei.com>; lorenzo.pieralisi@arm.com;
> > joro@8bytes.org; robin.murphy@arm.com; wanghuiqiang
> > <wanghuiqiang@huawei.com>; Guohanjun (Hanjun Guo)
> > <guohanjun@huawei.com>; Sami.Mujawar@arm.com; jon@solid-run.com;
> > eric.auger@redhat.com
> > Subject: Re: [PATCH v3 09/10] iommu/arm-smmu: Get associated RMR info
> > and install bypass SMR
> >
> > On 20/04/2021 09:27, Shameer Kolothum wrote:
> > > From: Jon Nettleton <jon@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@solid-run.com>
> > > Signed-off-by: Shameer Kolothum
> > <shameerali.kolothum.thodi@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).
> >
> > 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)).
>
> Thanks Steve for taking a look and testing this on SMMUv2. My knowledge
> on SMMUv2 is limited an don't have a setup to verify this. After reading
> the code, agree that the current implementation addresses the hardware
> configuration only and breaks all the scenarios explained above.
>
> I will include the below snippet in next respin if that works.
>
> Hi Jon,
>
> Could you please take a look and see the below changes works for
> you too?

My original code was derived from a solution that was proposed for
device-tree booted systems.  I will review and test the changes and
then report back.

-Jon


>
> Thanks,
> Shameer
>
> > ----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");
> > }