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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 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> <20230407113737-mutt-send-email-mst@kernel.org> <20230410060842-mutt-send-email-mst@kernel.org> <460d2724-5c92-da5c-2f8c-cf29ea6d8080@nvidia.com> <20230410154959-mutt-send-email-mst@kernel.org> From: Parav Pandit In-Reply-To: <20230410154959-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: SN7PR04CA0151.namprd04.prod.outlook.com (2603:10b6:806:125::6) To PH0PR12MB5481.namprd12.prod.outlook.com (2603:10b6:510:d4::15) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: PH0PR12MB5481:EE_|CH2PR12MB4295:EE_ X-MS-Office365-Filtering-Correlation-Id: b44671c0-e0f4-40ca-ee64-08db3a008735 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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Tsirkin wrote: > On Mon, Apr 10, 2023 at 10:34:16AM -0400, Parav Pandit wrote: >>> A device MUST offer VIRTIO_F_VERSION_1. A device MAY fail to operate further >>> if VIRTIO_F_VERSION_1 is not accepted. >>> >>> it's implied that this does not refer to legacy interface. >>> >> But the interface being exposes is not a legacy interface at the PCI device >> level. >> >> A PCI device is exposing a interface that can be used >> by either >> a. existing non transitional driver who will negotiate _1, just fine. >> or >> b. by legacy driver in the guest VM, which will not negotiate _1. >> >> And here device must not fail to operate. >> Hence spec should say that it should not fail to operate. > > sorry, what? it's exactly the legacy interface that's the whole > value of this hack, just exposed through another bar. > I am aligned with you on this part of exposing legacy interface via another bar (or a window within an existing memory bar). What is translates to is a spec wording something like below: A non transitional device exposes legacy interface using a memory mapped registers in a BAR or its parent PCI device through AQ. Legacy common configuration registers and device specific registers accessed through such interface work as legacy interface defined in rest of the specification. >> And since the guest driver may be 1.x, _1 will be offered by the device. > > _1 is not offered in the legacy interface. And if you negotiate Right. > _1 you better not touch legacy with a 10 foot pole. > Right. > Just add a new capability and explain that it exposes > the legacy interface in a window at an offset inside a memory bar. > that is mostly it. if there's an adapting layer that forwards > IO requests from legacy driver to that window, this allows this > driver to work and use the device through the legacy > interface. > ok. Something like above? > > There could be a small patch or two on top to tweak wording if there are > places where it says "non transitional devices have no legacy > interfaces". And probably an explicit list of devices > which are allowed to have this capability. > Make sense to me. effectively we will have, 1. one or two patches, as you describe in above point for tweaking wording + device list. 2. new optional capability (in extended area because legacy area is near to full). a. indicates it supports memory mapped and/or b. via aq (when aq is ready) 3. patch to make use of notification region as done in patch-10. --------------------------------------------------------------------- To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org