Re: [PATCH v3 3/3] arm-smmu: select suitable MSI IOVA

[Jason Gunthorpe]

On Wed, Aug 06, 2025 at 02:55:39PM -0700, Shyam Saini wrote:
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> @@ -3642,17 +3642,30 @@ static int arm_smmu_of_xlate(struct device *dev,
>  static void arm_smmu_get_resv_regions(struct device *dev,
>                                     struct list_head *head)
>  {
> -     struct iommu_resv_region *region;
>       int prot = IOMMU_WRITE | IOMMU_NOEXEC | IOMMU_MMIO;
>  
> -     region = iommu_alloc_resv_region(MSI_IOVA_BASE, MSI_IOVA_LENGTH,
> -                                      prot, IOMMU_RESV_SW_MSI, GFP_KERNEL);
> -     if (!region)
> -             return;
> -
> -     list_add_tail(&region->list, head);
> +     static const u64 msi_bases[] = { MSI_IOVA_BASE, MSI_IOVA_BASE2 };
>  
>       iommu_dma_get_resv_regions(dev, head);
> +
> +     /*
> +      * Use the first msi_base that does not intersect with a platform
> +      * reserved region. The SW MSI base selection is entirely arbitrary.
> +      */
> +     for (int i = 0; i != ARRAY_SIZE(msi_bases); i++) {
> +             struct iommu_resv_region *region;
> +
> +             if (resv_region_intersects(msi_bases[i], MSI_IOVA_LENGTH, head))
> +                     continue;
> +
> +             region = iommu_alloc_resv_region(msi_bases[i], MSI_IOVA_LENGTH, 
> prot,
> +                                              IOMMU_RESV_SW_MSI, GFP_KERNEL);
> +             if (!region)
> +                     return;
> +
> +             list_add_tail(&region->list, head);
> +             return;
> +     }
>  }

I think this whole series looks pretty good, but I would suggest to
put this in a helper..

'iommu_set_sw_msi()' perhaps, must be called after iommu_dma_get_resv_regions()

Then maybe the constants can just be placed in the .c file inside the
helper function.

Jsaon