Re: [PATCH] iommu/arm-smmu-qcom: Work around SDM845 Adreno SMMU w/ 16K pages

[Dmitry Baryshkov]

On Tue, 30 Jul 2024 at 00:08, Rob Clark <robdclark@xxxxxxxxx> wrote:
>
> On Mon, Jul 29, 2024 at 1:14 PM Dmitry Baryshkov
> <dmitry.baryshkov@xxxxxxxxxx> wrote:
> >
> > On Mon, Jul 29, 2024 at 10:37:48AM GMT, Konrad Dybcio wrote:
> > > From: Konrad Dybcio <konrad.dybcio@xxxxxxxxxx>
> > >
> > > SDM845's Adreno SMMU is unique in that it actually advertizes support
> > > for 16K (and 32M) pages, which doesn't hold for newer SoCs.
> > >
> > > This however, seems either broken in the hardware implementation, the
> > > hypervisor middleware that abstracts the SMMU, or there's a bug in the
> > > Linux kernel somewhere down the line that nobody managed to track down.
> > >
> > > Booting SDM845 with 16K page sizes and drm/msm results in:
> > >
> > > *** gpu fault: ttbr0=0000000000000000 iova=000100000000c000 dir=READ
> > > type=TRANSLATION source=CP (0,0,0,0)
> > >
> > > right after loading the firmware. The GPU then starts spitting out
> > > illegal intstruction errors, as it's quite obvious that it got a
> > > bogus pointer.
> > >
> > > Hide 16K support on SDM845's Adreno SMMU to work around this.
> > >
> > > Reported-by: Sumit Semwal <sumit.semwal@xxxxxxxxxx>
> > > Signed-off-by: Konrad Dybcio <konrad.dybcio@xxxxxxxxxx>
> > > ---
> > > There's a mismatch in sender/committer addresses but that's "fine":
> > > https://lore.kernel.org/linux-usb/2024072734-scenic-unwilling-71ea@gregkh/
> > > ---
> > >  drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c | 10 ++++++++++
> > >  1 file changed, 10 insertions(+)
> > >
> > > diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
> > > index 36c6b36ad4ff..d25825c05817 100644
> > > --- a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
> > > +++ b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
> > > @@ -338,6 +338,15 @@ static int qcom_smmu_cfg_probe(struct arm_smmu_device *smmu)
> > >       return 0;
> > >  }
> > >
> > > +static int qcom_adreno_smmuv2_cfg_probe(struct arm_smmu_device *smmu)
> > > +{
> > > +     /* SDM845 Adreno SMMU advertizes 16K pages support, but something is broken */
> > > +     if (of_device_is_compatible(smmu->dev->of_node, "qcom,sdm845-smmu-v2"))
> > > +             smmu->features &= ~ARM_SMMU_FEAT_FMT_AARCH64_16K;
> >
> > Shouldn't we hide that uncoditionally as it's likely that none of v2
> > Adreno SMMUs support 16k pages?
>
> Hmm, that would be unfortunate to have the GPU not supporting the CPU
> page size.  I guess we could still map 16k pages as multiple 4k pages,
> but that is a bit sad..

For now this might be limited to older platforms (v2 vs -500)

>
> BR,
> -R
>
> >
> > > +
> > > +     return 0;
> > > +}
> > > +
> > >  static void qcom_smmu_write_s2cr(struct arm_smmu_device *smmu, int idx)
> > >  {
> > >       struct arm_smmu_s2cr *s2cr = smmu->s2crs + idx;
> > > @@ -436,6 +445,7 @@ static const struct arm_smmu_impl sdm845_smmu_500_impl = {
> > >
> > >  static const struct arm_smmu_impl qcom_adreno_smmu_v2_impl = {
> > >       .init_context = qcom_adreno_smmu_init_context,
> > > +     .cfg_probe = qcom_adreno_smmuv2_cfg_probe,
> > >       .def_domain_type = qcom_smmu_def_domain_type,
> > >       .alloc_context_bank = qcom_adreno_smmu_alloc_context_bank,
> > >       .write_sctlr = qcom_adreno_smmu_write_sctlr,
> > >
> > > ---
> > > base-commit: 931a3b3bccc96e7708c82b30b2b5fa82dfd04890
> > > change-id: 20240726-topic-845_gpu_smmu-ab738f7a013c
> > >
> > > Best regards,
> > > --
> > > Konrad Dybcio <konradybcio@xxxxxxxxxx>
> > >
> >
> > --
> > With best wishes
> > Dmitry



-- 
With best wishes
Dmitry