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

[Dmitry Baryshkov]

On Tue, 30 Jul 2024 at 11:08, Konrad Dybcio <konradybcio@xxxxxxxxx> wrote:
>
> On 29.07.2024 11:21 PM, Dmitry Baryshkov wrote:
> > 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)
>
> In the commit message:
>
> >>>> SDM845's Adreno SMMU is unique in that it actually advertizes support
> >>>> for 16K (and 32M) pages, which doesn't hold for newer SoCs.

My question is about forbidding 16k pages for sdm845 only or for other
chips too. I'd assume that it shouldn't also work for other smmu-v2
platforms.

-- 
With best wishes
Dmitry