Re: [PATCH 2/5] iommu: sun50i: allocate page tables from below 4 GiB

[Robin Murphy <robin.murphy@arm.com>]

On 2024-05-31 12:37 am, Andre Przywara wrote:
> The Allwinner IOMMU is a strict 32-bit device, with the page table root
> pointer as well as both level's page tables and also the target addresses
> all required to be below 4GB.
> The Allwinner H6 SoC only supports 32-bit worth of physical addresses
> anyway, so this isn't a problem so far, but the H616 and later SoCs extend
> the PA space beyond 32 bit to accommodate more DRAM.
> To make sure we stay within the 32-bit PA range required by the IOMMU,
> force the memory for the page tables to come from below 4GB. by using
> allocations with the DMA32 flag.

Uh-oh... what about the output addresses in sun50i_mk_pte()? Limiting 
its own accesses is OK, but if the IOMMU isn't capable of *mapping* any 
valid PA for its clients, we can't easily support that.

Thanks,
Robin.

> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
> ---
>   drivers/iommu/sun50i-iommu.c | 5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iommu/sun50i-iommu.c b/drivers/iommu/sun50i-iommu.c
> index dd3f07384624c..c3244db5ac02f 100644
> --- a/drivers/iommu/sun50i-iommu.c
> +++ b/drivers/iommu/sun50i-iommu.c
> @@ -682,7 +682,8 @@ sun50i_iommu_domain_alloc_paging(struct device *dev)
>   	if (!sun50i_domain)
>   		return NULL;
>   
> -	sun50i_domain->dt = iommu_alloc_pages(GFP_KERNEL, get_order(DT_SIZE));
> +	sun50i_domain->dt = iommu_alloc_pages(GFP_KERNEL | GFP_DMA32,
> +					      get_order(DT_SIZE));
>   	if (!sun50i_domain->dt)
>   		goto err_free_domain;
>   
> @@ -997,7 +998,7 @@ static int sun50i_iommu_probe(struct platform_device *pdev)
>   
>   	iommu->pt_pool = kmem_cache_create(dev_name(&pdev->dev),
>   					   PT_SIZE, PT_SIZE,
> -					   SLAB_HWCACHE_ALIGN,
> +					   SLAB_HWCACHE_ALIGN | SLAB_CACHE_DMA32,
>   					   NULL);
>   	if (!iommu->pt_pool)
>   		return -ENOMEM;