> From: Tian, Kevin <kevin.tian@xxxxxxxxx>
> Sent: Thursday, March 16, 2023 4:17 PM
>
> > From: Liu, Yi L <yi.l.liu@xxxxxxxxx>
> > 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 pasid
> > * will 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@xxxxxxxxxx/
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
