Messages in this thread | | | Date | Mon, 7 Aug 2023 21:14:24 +0100 | Subject | Re: [PATCH v3 5.15 4/6] iommu/arm-smmu-v3: Document MMU-700 erratum 2812531 | From | Robin Murphy <> |
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On 2023-08-02 18:02, Easwar Hariharan wrote: > From: Robin Murphy <robin.murphy@arm.com> > > commit 309a15cb16bb075da1c99d46fb457db6a1a2669e upstream > > To work around MMU-700 erratum 2812531 we need to ensure that certain > sequences of commands cannot be issued without an intervening sync. In > practice this falls out of our current command-batching machinery > anyway - each batch only contains a single type of invalidation command, > and ends with a sync. The only exception is when a batch is sufficiently > large to need issuing across multiple command queue slots, wherein the > earlier slots will not contain a sync and thus may in theory interleave > with another batch being issued in parallel to create an affected > sequence across the slot boundary. > > Since MMU-700 supports range invalidate commands and thus we will prefer > to use them (which also happens to avoid conditions for other errata), > I'm not entirely sure it's even possible for a single high-level > invalidate call to generate a batch of more than 63 commands,
Out of interest, have you observed a case where this actually happens?
> but for > the sake of robustness and documentation, wire up an option to enforce > that a sync is always inserted for every slot issued. > > The other aspect is that the relative order of DVM commands cannot be > controlled, so DVM cannot be used. Again that is already the status quo, > but since we have at least defined ARM_SMMU_FEAT_BTM, we can explicitly > disable it for documentation purposes even if it's not wired up anywhere > yet.
Note that there seems to be a slight issue with this patch that I missed, under discussion here:
https://lore.kernel.org/linux-iommu/27c895b8-1fb0-be88-8bc3-878d754684c8@huawei.com/T/#t
Thanks, Robin.
> Signed-off-by: Robin Murphy <robin.murphy@arm.com> > Reviewed-by: Nicolin Chen <nicolinc@nvidia.com> > Link: https://lore.kernel.org/r/330221cdfd0003cd51b6c04e7ff3566741ad8374.1683731256.git.robin.murphy@arm.com > Signed-off-by: Will Deacon <will@kernel.org> > Signed-off-by: Easwar Hariharan <eahariha@linux.microsoft.com> > --- > Documentation/arm64/silicon-errata.rst | 2 ++ > drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 12 ++++++++++++ > drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h | 1 + > 3 files changed, 15 insertions(+) > > diff --git a/Documentation/arm64/silicon-errata.rst b/Documentation/arm64/silicon-errata.rst > index 55e1e074dec1..322df8abbc0e 100644 > --- a/Documentation/arm64/silicon-errata.rst > +++ b/Documentation/arm64/silicon-errata.rst > @@ -124,6 +124,8 @@ stable kernels. > +----------------+-----------------+-----------------+-----------------------------+ > | ARM | MMU-600 | #1076982 | N/A | > +----------------+-----------------+-----------------+-----------------------------+ > +| ARM | MMU-700 | #2812531 | N/A | > ++----------------+-----------------+-----------------+-----------------------------+ > +----------------+-----------------+-----------------+-----------------------------+ > | Broadcom | Brahma-B53 | N/A | ARM64_ERRATUM_845719 | > +----------------+-----------------+-----------------+-----------------------------+ > diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c > index 782d040a829c..6a551a48d271 100644 > --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c > +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c > @@ -897,6 +897,12 @@ static void arm_smmu_cmdq_batch_add(struct arm_smmu_device *smmu, > struct arm_smmu_cmdq_batch *cmds, > struct arm_smmu_cmdq_ent *cmd) > { > + if (cmds->num == CMDQ_BATCH_ENTRIES - 1 && > + (smmu->options & ARM_SMMU_OPT_CMDQ_FORCE_SYNC)) { > + arm_smmu_cmdq_issue_cmdlist(smmu, cmds->cmds, cmds->num, true); > + cmds->num = 0; > + } > + > if (cmds->num == CMDQ_BATCH_ENTRIES) { > arm_smmu_cmdq_issue_cmdlist(smmu, cmds->cmds, cmds->num, false); > cmds->num = 0; > @@ -3461,6 +3467,7 @@ static int arm_smmu_device_reset(struct arm_smmu_device *smmu, bool bypass) > > #define IIDR_IMPLEMENTER_ARM 0x43b > #define IIDR_PRODUCTID_ARM_MMU_600 0x483 > +#define IIDR_PRODUCTID_ARM_MMU_700 0x487 > > static void arm_smmu_device_iidr_probe(struct arm_smmu_device *smmu) > { > @@ -3481,6 +3488,11 @@ static void arm_smmu_device_iidr_probe(struct arm_smmu_device *smmu) > if (variant == 0 && revision <= 2) > smmu->features &= ~ARM_SMMU_FEAT_SEV; > break; > + case IIDR_PRODUCTID_ARM_MMU_700: > + /* Arm erratum 2812531 */ > + smmu->features &= ~ARM_SMMU_FEAT_BTM; > + smmu->options |= ARM_SMMU_OPT_CMDQ_FORCE_SYNC; > + break; > } > break; > } > diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h > index 5964e02c4e57..abaecdf8d5d2 100644 > --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h > +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h > @@ -651,6 +651,7 @@ struct arm_smmu_device { > #define ARM_SMMU_OPT_SKIP_PREFETCH (1 << 0) > #define ARM_SMMU_OPT_PAGE0_REGS_ONLY (1 << 1) > #define ARM_SMMU_OPT_MSIPOLL (1 << 2) > +#define ARM_SMMU_OPT_CMDQ_FORCE_SYNC (1 << 3) > u32 options; > > struct arm_smmu_cmdq cmdq;
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