From: Tian, Kevin kevin.tian@intel.com Sent: Thursday, March 16, 2023 4:17 PM
From: Liu, Yi L yi.l.liu@intel.com Sent: Thursday, March 9, 2023 3:54 PM @@ -222,6 +223,11 @@ struct iommu_iotlb_gather { /**
- struct iommu_ops - iommu ops and capabilities
- @capable: check capability
- @hw_info: IOMMU hardware information. The type of the returned
data
is
defined in include/uapi/linux/iommufd.h. The data buffer is"The type of the returned data is marked by @driver_type".
"defined in include/uapi/linux/iommufd.h" should belong to the comment of @driver_type
Sure.
allocated in the IOMMU driver and the caller should free it
after use. Return the data buffer if success, or ERR_PTR on
failure.- @domain_alloc: allocate iommu domain
- @probe_device: Add device to iommu driver handling
- @release_device: Remove device from iommu driver handling
@@ -246,11 +252,17 @@ struct iommu_iotlb_gather {
- @remove_dev_pasid: Remove any translation configurations of a
specific
pasid, so that any DMA transactions with this pasidwill be blocked by the hardware.
- @driver_type: One of enum iommu_hw_info_type. This is used in the
hw_info
reporting path. For the drivers that supports it, a unique
type should be defined. For the driver that does not support
it, this field is the IOMMU_HW_INFO_TYPE_DEFAULT that is 0.
Hence, such drivers do not need to care this field.The meaning of "driver_type" is much broader than reporting hw_info.
let's be accurate to call it as "hw_info_type". and while we have two separate fields for one feature where is the check enforced on whether both are provided?
It is filled in the uapi structure by referring ops->driver_type in next patch.
Is it simpler to return the type directly in @hw_info?
Per the current description, if the iommu driver doesn't implement .hw_info callback, then it will not set driver_type field neither. Then this field is 0 (IOMMU_HW_INFO_TYPE_NONE). The GET_HW_INFO ioctl in next patch would fail as well. Under this implementation, returning the driver_type (a.k.a hw_info_type per your comment) in the hw_info callback may be simpler.
But I plan to update the implementation per the below remark from Jason. The GET_HW_INFO needs to succeed even if the underlying iommu driver does not implement hw_info callback. If so, it's still much more convenient to get the type by referring ops->driver_type.
https://lore.kernel.org/kvm/ZAcwJSK%2F9UVI9LXu@nvidia.com/
Also, per Nic's other remark, there would be a bitmap named hwpt_types field added to iommu_ops. Then it is also easier to referring it by ops->hwpt_types.
https://lore.kernel.org/linux-iommu/ZArgAXMUpNjDfFgZ@Asurada-Nvidia/#t
Surely, we also have another alternative. We can enforce all the iommu drivers to implement a minimum hw_info callback which just returns the driver_type if it does not have driver-specific data to report to the user yet.
btw IOMMU_HW_INFO_TYPE_DEFAULT also sounds misleading. 'default' implies hw_info still available but in a default format.
probably it's clearer to call it IOMMU_HW_INFO_TYPE_NONE.
Sure. Makes sense. So _NONE means no driver specific info is Reported back to user.
Regards, Yi Liu