From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: virtio-comment-return-1373-cohuck=redhat.com@lists.oasis-open.org Sender: List-Post: List-Help: List-Unsubscribe: List-Subscribe: Received: from lists.oasis-open.org (oasis-open.org [10.110.1.242]) by lists.oasis-open.org (Postfix) with ESMTP id 9571B985B4C for ; Mon, 27 Jul 2020 13:56:47 +0000 (UTC) Date: Mon, 27 Jul 2020 09:56:39 -0400 From: "Michael S. Tsirkin" Message-ID: <20200727095239-mutt-send-email-mst@kernel.org> References: <20200727091802-mutt-send-email-mst@kernel.org> <85f69f31-e4c6-e7af-1fa5-90e5a2c81ae8@siemens.com> MIME-Version: 1.0 In-Reply-To: <85f69f31-e4c6-e7af-1fa5-90e5a2c81ae8@siemens.com> Subject: Re: [virtio-comment] Re: [RFC] ivshmem v2: Shared memory device specification Content-Type: text/plain; charset=us-ascii Content-Disposition: inline To: Jan Kiszka Cc: "virtio-comment@lists.oasis-open.org" , Jailhouse , qemu-devel , Alex =?iso-8859-1?Q?Benn=E9e?= , liang yan List-ID: On Mon, Jul 27, 2020 at 03:39:32PM +0200, Jan Kiszka wrote: > On 27.07.20 15:20, Michael S. Tsirkin wrote: > > On Mon, May 25, 2020 at 09:58:28AM +0200, Jan Kiszka wrote: > > > #### Vendor Specific Capability (ID 09h) > > > > > > This capability must always be present. > > > > > > | Offset | Register | Content | > > > |-------:|:--------------------|:-----------------------------------------------| > > > | 00h | ID | 09h | > > > | 01h | Next Capability | Pointer to next capability or 00h | > > > | 02h | Length | 20h if Base Address is present, 18h otherwise | > > > | 03h | Privileged Control | Bit 0 (read/write): one-shot interrupt mode | > > > | | | Bits 1-7: Reserved (0 on read, writes ignored) | > > > | 04h | State Table Size | 32-bit size of read-only State Table | > > > | 08h | R/W Section Size | 64-bit size of common read/write section | > > > | 10h | Output Section Size | 64-bit size of output sections | > > > | 18h | Base Address | optional: 64-bit base address of shared memory | > > > > > > All registers are read-only. Writes are ignored, except to bit 0 of > > > the Privileged Control register. > > > > > > Is there value in making this follow the virtio vendor-specific > > capability format? That will cost several extra bytes - do you envision > > having many of these in the config space? > > Of course, this could be modeled with via virtio_pci_cap as well. Would add > 12 unused by bytes and one type byte. If it helps to make the device look > more virtio'ish, but I'm afraid there are more differences at PCI level. I guess it will be useful if we ever find it handy to make an ivshmem device also be a virtio device. Can't say why yet but if we don't care it vaguely seems kind of like a good idea. I guess it will also be handy if you ever need another vendor specific cap: you already get a way to identify it without breaking drivers. > I do not see a use case for having multiple of those caps above per device. > If someone comes around with a valid use case for having multiple, > non-consequitive shared memory regions for one device, we would need to add > registers for them. But that would also only work for non-BAR regions due to > limited BARs. OK, I guess this answers the below too. > > Also, do we want to define an extended capability format in case this > > is a pci extended capability? > > > > What would be the practical benefit? Do you see PCIe caps that could become > useful in virtual setups? So if we ever have a huge number of these caps, PCIe allows many more caps. > We don't do that for regular virtio devices > either, do we? We don't, there's a small number of these so we don't run out of config space. > > Thanks, > Jan > > -- > Siemens AG, Corporate Technology, CT RDA IOT SES-DE > Corporate Competence Center Embedded Linux This publicly archived list offers a means to provide input to the OASIS Virtual I/O Device (VIRTIO) TC. In order to verify user consent to the Feedback License terms and to minimize spam in the list archive, subscription is required before posting. Subscribe: virtio-comment-subscribe@lists.oasis-open.org Unsubscribe: virtio-comment-unsubscribe@lists.oasis-open.org List help: virtio-comment-help@lists.oasis-open.org List archive: https://lists.oasis-open.org/archives/virtio-comment/ Feedback License: https://www.oasis-open.org/who/ipr/feedback_license.pdf List Guidelines: https://www.oasis-open.org/policies-guidelines/mailing-lists Committee: https://www.oasis-open.org/committees/virtio/ Join OASIS: https://www.oasis-open.org/join/