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

[Vivek Gautam <vivek.gautam@codeaurora.org>]

Hi Bjorn,


On Mon, Sep 10, 2018 at 4:08 PM Vivek Gautam
<vivek.gautam@codeaurora.org> wrote:
>
> +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].

Gentle ping. Please let me know if you have comments on the SCM pieces
in this series.

Thanks & Regards
Vivek

> >
> > 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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