RE: [PATCH v4 2/4] iommu: Add new iommu op to get iommu hardware information

[Tian, Kevin]

> From: Liu, Yi L <yi.l.liu@xxxxxxxxx>
> Sent: Monday, July 24, 2023 7:00 PM
> 
> @@ -252,11 +258,20 @@ 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.
> + * @hw_info_type: One of enum iommu_hw_info_type defined in
> + *                include/uapi/linux/iommufd.h. It is used to tag the type
> + *                of data returned by .hw_info callback. The drivers that
> + *                support .hw_info callback should define a unique type
> + *                in include/uapi/linux/iommufd.h. For the drivers that do
> + *                not implement .hw_info callback, this field is
> + *                IOMMU_HW_INFO_TYPE_NONE which is 0. Hence, such drivers
> + *                do not need to care this field.

every time looking at this field the same question came out why it is required
(and looks I forgot your previous response).

e.g. why cannot the type be returned in @hw_info():

	void *(*hw_info)(struct device *dev, u32 *length, int *type);

NULL callback implies IOMMU_HW_INFO_TYPE_NONE.

otherwise if there is a reason could you update the commit msg to reflect
it so I don't need to ask again next time? 😊