linux-kernel - RE: [PATCH v2 2/4] iommu: Add new iommu op to get iommu hardware information

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Date:   Thu, 16 Mar 2023 08:16:35 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     "Liu, Yi L" <yi.l.liu@...el.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "jgg@...dia.com" <jgg@...dia.com>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>
CC:     "cohuck@...hat.com" <cohuck@...hat.com>,
        "eric.auger@...hat.com" <eric.auger@...hat.com>,
        "nicolinc@...dia.com" <nicolinc@...dia.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "mjrosato@...ux.ibm.com" <mjrosato@...ux.ibm.com>,
        "chao.p.peng@...ux.intel.com" <chao.p.peng@...ux.intel.com>,
        "yi.y.sun@...ux.intel.com" <yi.y.sun@...ux.intel.com>,
        "peterx@...hat.com" <peterx@...hat.com>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        "shameerali.kolothum.thodi@...wei.com" 
        <shameerali.kolothum.thodi@...wei.com>,
        "lulu@...hat.com" <lulu@...hat.com>,
        "suravee.suthikulpanit@....com" <suravee.suthikulpanit@....com>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>
Subject: RE: [PATCH v2 2/4] iommu: Add new iommu op to get iommu hardware
 information

> From: Liu, Yi L <yi.l.liu@...el.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

> + *           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?

Is it simpler to return the type directly in @hw_info?

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.