Re: [PATCH v4 3/3] iommu: Drop sw_msi from iommu_domain

[Jason Gunthorpe]

On Mon, Mar 24, 2025 at 10:07:43AM -0700, Nathan Chancellor wrote:

> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 0f4cc15ded1c..2b81166350ae 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -3661,7 +3661,6 @@ int iommu_dma_prepare_msi(struct msi_desc *desc, phys_addr_t msi_addr)
>  			ret = iommufd_sw_msi(group->domain, desc, msi_addr);
>  			break;
>  		default:
> -			ret = -EOPNOTSUPP;
>  			break;
>  		}
>  	}

Can we explain why this scenario has a 0 cookie_type?

Actually.. Is it just an identity domain? Nicolin did you test this on
your arm system with a device using identity (iommu=pt kernel param)?
I would expect identity to end up with a 0 cookie because we never
setup dma-iommu.c code on it.

Should we be testing for identity to return 0 instead?

Jason