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

[Konrad Dybcio]

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.

Konrad