Re: [PATCH v4 3/6] iommu: Add return value rules to attach_dev op and APIs

[Baolu Lu <baolu.lu@linux.intel.com>]

On 9/21/22 4:23 PM, Nicolin Chen wrote:
> Cases like VFIO wish to attach a device to an existing domain that was
> not allocated specifically from the device. This raises a condition
> where the IOMMU driver can fail the domain attach because the domain and
> device are incompatible with each other.
> 
> This is a soft failure that can be resolved by using a different domain.
> 
> Provide a dedicated errno EINVAL from the IOMMU driver during attach that
> the reason why the attach failed is because of domain incompatibility.
> 
> VFIO can use this to know that the attach is a soft failure and it should
> continue searching. Otherwise, the attach will be a hard failure and VFIO
> will return the code to userspace.
> 
> Update kdocs to add rules of return value to the attach_dev op and APIs.
> 
> Suggested-by: Jason Gunthorpe<jgg@nvidia.com>
> Signed-off-by: Nicolin Chen<nicolinc@nvidia.com>
> ---
>   drivers/iommu/iommu.c | 22 ++++++++++++++++++++++
>   include/linux/iommu.h | 12 ++++++++++++
>   2 files changed, 34 insertions(+)
> 
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 3a808146b50f..1d1e32aeaae6 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -1975,6 +1975,17 @@ static int __iommu_attach_device(struct iommu_domain *domain,
>   	return ret;
>   }
>   
> +/**
> + * iommu_attach_device - Attach a device to an IOMMU domain

Normally we say "attach an iommu domain to a device/group ...".

Best regards,
baolu