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    SubjectRe: [PATCH v3 5.15 4/6] iommu/arm-smmu-v3: Document MMU-700 erratum 2812531
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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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