Re: [PATCH] iommu: arm-smmu: Fix Tegra workaround for PAGE_SIZE mappings

[Ashish Mhetre <amhetre@nvidia.com>]

On 7/23/2024 9:41 PM, Will Deacon wrote:
> External email: Use caution opening links or attachments
>
>
> On Wed, Jul 17, 2024 at 07:21:45AM +0000, Ashish Mhetre wrote:
>> PAGE_SIZE can be 16KB for Tegra which is not supported by MMU-500 on
>> both Tegra194 and Tegra234. So, use 4KB mappings when PAGE_SIZE is 16KB.
>>
>> Signed-off-by: Ashish Mhetre <amhetre@nvidia.com>
>> ---
>>   drivers/iommu/arm/arm-smmu/arm-smmu-nvidia.c | 5 +++--
>>   1 file changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu-nvidia.c b/drivers/iommu/arm/arm-smmu/arm-smmu-nvidia.c
>> index 4b2994b6126d..bb621a94f6fe 100644
>> --- a/drivers/iommu/arm/arm-smmu/arm-smmu-nvidia.c
>> +++ b/drivers/iommu/arm/arm-smmu/arm-smmu-nvidia.c
>> @@ -273,11 +273,12 @@ static int nvidia_smmu_init_context(struct arm_smmu_domain *smmu_domain,
>>         * release of PMD entry and avoid translations seeing stale PMD entry in
>>         * walk cache.
>>         * Fix this by limiting the page mappings to PAGE_SIZE on Tegra194 and
>> -      * Tegra234.
>> +      * Tegra234. Use 4K page mappings if PAGE_SIZE is 16K as MMU500 doesn't
>> +      * support it.
>>         */
>>        if (of_device_is_compatible(np, "nvidia,tegra234-smmu") ||
>>            of_device_is_compatible(np, "nvidia,tegra194-smmu")) {
>> -             smmu->pgsize_bitmap = PAGE_SIZE;
>> +             smmu->pgsize_bitmap = (PAGE_SIZE == SZ_16K) ? SZ_4K : PAGE_SIZE;
> Perhaps it would be more robust to do a read-modify-write of the
> pgsize_bitmap, preserving all the page-sizes that are <= PAGE_SIZE (i.e.
> and it with something like GENMASK(PAGE_SHIFT, 0)?
>
> Will


Thanks for the review Will. Yes, that will be a better approach as
pgsize_bitmap will never be with 16K granularity for Tegra.
I will send new version with this update.