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Tsirkin" CC: "virtio-dev@lists.oasis-open.org" , "cohuck@redhat.com" , "virtio-comment@lists.oasis-open.org" , Shahaf Shuler , Satananda Burla Thread-Topic: [virtio-comment] Re: [PATCH 07/11] transport-pci: Introduce transitional MMR device id Thread-Index: AQHZY1tHbf+nicr9uUaxzLNq1cXcgq8ax2UAgACRZQCABHJagIAALYOw Date: Fri, 7 Apr 2023 15:18:47 +0000 Message-ID: References: <20230330225834.506969-1-parav@nvidia.com> <20230330225834.506969-8-parav@nvidia.com> <20230404032700-mutt-send-email-mst@kernel.org> <94b217ee-29d9-42da-f2b8-28ced7e64371@nvidia.com> <20230407074605-mutt-send-email-mst@kernel.org> In-Reply-To: <20230407074605-mutt-send-email-mst@kernel.org> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: authentication-results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=nvidia.com; x-ms-publictraffictype: Email x-ms-traffictypediagnostic: PH0PR12MB5481:EE_|SJ0PR12MB8116:EE_ x-ms-office365-filtering-correlation-id: ed10a71d-55b1-4e96-a821-08db377b629c x-ms-exchange-senderadcheck: 1 x-ms-exchange-antispam-relay: 0 x-microsoft-antispam: BCL:0; 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charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: PH0PR12MB5481.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: ed10a71d-55b1-4e96-a821-08db377b629c X-MS-Exchange-CrossTenant-originalarrivaltime: 07 Apr 2023 15:18:47.7814 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: sTlwP0FPGh6Cq6LrvafOV2rSZ22TwGyGVctzDAIe2fhlNUUu+3+NMd+hg6wvdhzTH2NH/X9cuVmxxdBDJGoLXg== X-MS-Exchange-Transport-CrossTenantHeadersStamped: SJ0PR12MB8116 Subject: RE: [virtio-comment] Re: [PATCH 07/11] transport-pci: Introduce transitional MMR device id > From: Michael S. Tsirkin > Sent: Friday, April 7, 2023 8:03 AM >=20 > On Tue, Apr 04, 2023 at 12:08:54PM -0400, Parav Pandit wrote: [..] > > > I took a fresh look at it, and I don't get it: what exactly is wrong > > > with just using modern ID? Why do we need new ones? > > > > A modern (non transitional device) do not support legacy functionality > > such as virtio net hdr, >=20 > It's all a question of terminology, but it is not worth sacrificing funct= ionality for > cleaner terminology. > Basically most of the spec just talks about the legacy interface, and wil= l work > fine with this. >=20 > Yes we do say: > Devices or drivers with no legacy compatibility are referred to as non- > transitional devices and drivers, respectively. >=20 >=20 > So we will want to refine this somewhat. Maybe: >=20 > Devices not compatible with legacy drivers and drivers not compatible > with legacy devices are referred to as non-transitional devices and > drivers, respectively. >=20 >=20 > This allows non-transitional devices to expose the legacy capability - ha= ving this > capability does not make them compatible with >=20 > Similarly in the conformance section: >=20 > An implementation MAY choose to implement OPTIONAL support for the > legacy interface, including support for legacy drivers or devices, by con= forming > to all of the MUST or REQUIRED level requirements for the legacy interfac= e for > the transitional devices and drivers. >=20 > we would just remove "for the transitional devices and drivers" > here as now non-transitional can have a legacy interface. >=20 > Similarly: >=20 > The requirements for the legacy interface for transitional implementation= s >=20 > would become: >=20 > "The requirements for the legacy interface" >=20 > I will hold to respond to other emails in this series, because the key part= is here. If I understand you correctly, will above wording translate to below behavi= or? 1. A non-transitional device will expose a capability (not a feature bit, b= ut a capability at transport level). This capability indicates that, it supports legacy interface. Lets name it legacy_if_emulation for sake of this discussion. It is a two-way pci capability. Device reports it. And driver enables it. (Why two way and why driver needs to enable it, desc= ribed later in point #d below). Hence, such non transitional device does not need to comply to below listed= requirements #a and #b. a. A driver MUST accept VIRTIO_F_VERSION_1 if it is offered. (Because hypervisor driver is a passthrough driver; and legacy driver will = not accept this feature bit). b. device MAY fail to operate further if VIRTIO_F_VERSION_1 is not accepted= . c. A non-transitional device with above legacy_if_supported capability, wil= l allow device reset sequence, described in [1] Driver Requirements: Device Initialization (3.1.1) [2] Legacy Interface: Device Initialization (3.1.2) > > device reset sequence. >=20 > what is this one? I listed above in #c. And=20 d. When legacy_if_emulation capability is offered and hypervisor driver ena= bled it, when driver perform device reset, driver will not wait for device = reset to go zero. When legacy_if_emulation capability is not enabled by (hypervisor or other = say existing) driver, driver will wait for device reset to turn 0. (Followi= ng the driver requirement 2.4.2). 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