Re: [PATCH v5 7/8] iommu/arm-smmu: Get associated RMR info and install bypass SMR

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

On Thu, Jun 3, 2021 at 1:27 PM Steven Price <steven.price@arm.com> wrote:
>
> On 03/06/2021 09:52, Jon Nettleton wrote:
> > On Mon, May 24, 2021 at 1:04 PM Shameer Kolothum
> > <shameerali.kolothum.thodi@huawei.com> 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: Steven Price <steven.price@arm.com>
> >> Signed-off-by: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
> >> ---
> >>  drivers/iommu/arm/arm-smmu/arm-smmu.c | 65 +++++++++++++++++++++++++++
> >>  1 file changed, 65 insertions(+)
> >>
> >> diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu.c b/drivers/iommu/arm/arm-smmu/arm-smmu.c
> >> index 6f72c4d208ca..56db3d3238fc 100644
> >> --- a/drivers/iommu/arm/arm-smmu/arm-smmu.c
> >> +++ b/drivers/iommu/arm/arm-smmu/arm-smmu.c
> >> @@ -2042,6 +2042,67 @@ err_reset_platform_ops: __maybe_unused;
> >>         return err;
> >>  }
> >>
> >> +static void arm_smmu_rmr_install_bypass_smr(struct arm_smmu_device *smmu)
> >> +{
> >> +       struct list_head rmr_list;
> >> +       struct iommu_resv_region *e;
> >> +       int i, cnt = 0;
> >> +       u32 smr;
> >> +       u32 reg;
> >> +
> >> +       INIT_LIST_HEAD(&rmr_list);
> >> +       if (iommu_dma_get_rmrs(dev_fwnode(smmu->dev), &rmr_list))
> >> +               return;
> >> +
> >> +       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, &rmr_list, list) {
> >> +               u32 sid = e->fw_data.rmr.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;
>
> Looking at this code again, that mask looks wrong! According to the SMMU
> spec MASK[i]==1 means ID[i] is ignored. I.e. this means completely
> ignore the ID...
>
> I'm not at all sure why they designed the hardware that way round.
>
> >> +                       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");
> >> +       iommu_dma_put_rmrs(dev_fwnode(smmu->dev), &rmr_list);
> >> +}
> >> +
> >>  static int arm_smmu_device_probe(struct platform_device *pdev)
> >>  {
> >>         struct resource *res;
> >> @@ -2168,6 +2229,10 @@ static int arm_smmu_device_probe(struct platform_device *pdev)
> >>         }
> >>
> >>         platform_set_drvdata(pdev, smmu);
> >> +
> >> +       /* Check for RMRs and install bypass SMRs if any */
> >> +       arm_smmu_rmr_install_bypass_smr(smmu);
> >> +
> >>         arm_smmu_device_reset(smmu);
> >>         arm_smmu_test_smr_masks(smmu);
> >>
> >> --
> >> 2.17.1
> >>
> >
> > Shameer and Robin
> >
> > I finally got around to updating edk2 and the HoneyComb IORT tables to
> > reflect the new standards.
> > Out of the box the new patchset was generating errors immediatly after
> > the smmu bringup.
> >
> > arm-smmu arm-smmu.0.auto: Unhandled context fault: fsr=0x402, iova=0x2080000140,
> > fsynr=0x1d0040, cbfrsynra=0x4000, cb=0
> >
> > These errors were generated even with disable_bypass=0
> >
> > I tracked down the issue to
> >
> > This code is skipped as Robin said would be correct
>
> If you're skipping the first bit of code, then that (hopefully) means
> that the SMMU is disabled...
>
> >> +       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;
> >> +               }[    2.707729] arm-smmu: setting up rmr list on 0x4000
> > [    2.712598] arm-smmu: s2crs count is 0 smrs index 0x0
> > [    2.717638] arm-smmu: s2crs count is 0 smrs id is 0x4000
> > [    2.722939] arm-smmu: s2crs count is 0 smrs mask is 0x8000
> > [    2.728417] arm-smmu arm-smmu.0.auto:        preserved 1 boot mapping
> >
> >> +       }
> >
> > Then this code block was hit which is correct
> >
> >> +               if (smmu->s2crs[i].count == 0) {
> >> +                       smmu->smrs[i].id = sid;
> >> +                       smmu->smrs[i].mask = ~0;
> >> +                       smmu->smrs[i].valid = true;
> >> +               }
> >
> > The mask was causing the issue.  If I think ammended that segment to read
> > the mask as setup by the hardware everything was back to functioning both
> > with and without disable_bypass set.
>
> ...so reading a mask from it doesn't sounds quite right.
>
> Can you have a go with a corrected mask of '0' rather than all-1s and
> see if that helps? My guess is that the mask of ~0 was causing multiple
> matches in the SMRs which is 'UNPREDICTABLE'.
>
> Sadly in my test setup there's only the one device behind the SMMU so
> I didn't spot this (below patch works for me, but that's not saying
> much).
>
> Steve
>
> --->8---
> diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu.c b/drivers/iommu/arm/arm-smmu/arm-smmu.c
> index 56db3d3238fc..44831d0c78e4 100644
> --- a/drivers/iommu/arm/arm-smmu/arm-smmu.c
> +++ b/drivers/iommu/arm/arm-smmu/arm-smmu.c
> @@ -2079,7 +2079,7 @@ static void arm_smmu_rmr_install_bypass_smr(struct arm_smmu_device *smmu)
>                         continue;
>                 if (smmu->s2crs[i].count == 0) {
>                         smmu->smrs[i].id = sid;
> -                       smmu->smrs[i].mask = ~0;
> +                       smmu->smrs[i].mask = 0;
>                         smmu->smrs[i].valid = true;
>                 }
>                 smmu->s2crs[i].count++;

Yes this works fine. Thanks