Re: [PATCH v2 0/4] Qcom smmu-500 TLB invalidation errata for sdm845

[Vivek Gautam]

+linux-arm-msm


On 09/10/2018 11:55 AM, Vivek Gautam wrote:
> Qcom's implementation of arm,mmu-500 on sdm845 has a functional/performance
> errata [1] because of which the TCU cache look ups are stalled during
> invalidation cycle. This is mitigated by serializing all the invalidation
> requests coming to the smmu.
>
> This patch series addresses this errata by adding new tlb_ops for
> qcom,sdm845-smmu-500 [2]. These ops take context bank locks for all the
> tlb_ops that queue and sync the TLB invalidation requests.
>
> Besides adding locks, there's a way to expadite these TLB invalidations
> for display and camera devices by turning off the 'wait-for-safe' logic
> in hardware that holds the tlb invalidations until a safe level.
> This 'wait-for-safe' logic is controlled by toggling a chicken bit
> through a secure register. This secure register is accessed by making an
> explicit SCM call into the EL3 firmware.
> There are two ways of handling this logic -
>   * Firmware, such as tz present on sdm845-mtp devices has a handler to do
>     all the register access and bit set/clear. So is the handling in
>     downstream arm-smmu driver [3].
>   * Other firmwares can have handlers to just read/write this secure
>     register. In such cases the kernel make io_read/writel scm calls to
>     modify the register.
> This patch series adds APIs in qcom-scm driver to handle both of these
> cases.
>
> Lastly, since these TLB invalidations can happen in atomic contexts
> there's a need to add atomic versions of qcom_scm_io_readl/writel() and
> qcom_scm_call() APIs. The traditional scm calls take mutex and we therefore
> can't use these calls in atomic contexts.
>
> This patch series is adapted version of how the errata is handled in
> downstream [1].
>
> Changes since v1:
>   * Addressed Will and Robin's comments:
>      - Dropped the patch[4] that forked out __arm_smmu_tlb_inv_range_nosync(),
>        and __arm_smmu_tlb_sync().
>      - Cleaned up the errata patch further to use downstream polling mechanism
>        for tlb sync.
>   * No change in SCM call patches - patches 1 to 3.
>
> [1] https://source.codeaurora.org/quic/la/kernel/msm-4.9/tree/drivers/iommu/arm-smmu.c?h=msm-4.9#n4842
> [2] https://lore.kernel.org/patchwork/patch/974114/
> [3] https://source.codeaurora.org/quic/la/kernel/msm-4.9/tree/drivers/iommu/arm-smmu.c?h=msm-4.9#n4864
> [4] https://patchwork.kernel.org/patch/10565349/
>
> Vivek Gautam (4):
>    firmware: qcom_scm-64: Add atomic version of qcom_scm_call
>    firmware/qcom_scm: Add atomic version of io read/write APIs
>    firmware/qcom_scm: Add scm call to handle smmu errata
>    iommu/arm-smmu: Add support to handle Qcom's TLBI serialization errata
>
>   drivers/firmware/qcom_scm-32.c |  17 ++++
>   drivers/firmware/qcom_scm-64.c | 181 +++++++++++++++++++++++++++++++----------
>   drivers/firmware/qcom_scm.c    |  18 ++++
>   drivers/firmware/qcom_scm.h    |   9 ++
>   drivers/iommu/arm-smmu-regs.h  |   2 +
>   drivers/iommu/arm-smmu.c       | 133 +++++++++++++++++++++++++++++-
>   include/linux/qcom_scm.h       |   6 ++
>   7 files changed, 320 insertions(+), 46 deletions(-)

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