From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1907DC388F7 for ; Fri, 6 Nov 2020 03:12:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 925F72078E for ; Fri, 6 Nov 2020 03:12:18 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="LEuWal1Y" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725965AbgKFDMR (ORCPT ); Thu, 5 Nov 2020 22:12:17 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:26639 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725828AbgKFDMR (ORCPT ); Thu, 5 Nov 2020 22:12:17 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1604632335; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=mv+dLynp8wUq7v3ImjOM3aGT1sa91HyGF6RRHk9k3M0=; b=LEuWal1Yuqj61X+ScmEMcIBbVRo2Mj8Rqt/I+6JBVdHcG6wLw3Wc9y7e9uFulukL0SZHGx LZy1cSND9GMUQzFZeXdewVfYKmXXZVAL6QPffsK+JY1ZzdHjLjEY0/jmpPLZGMPHx7bRLB 0+0XDIxOdsA5vyc78/894zPF5dRkJaM= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-334-Pf1tyOvTPw2ub-3Qr7YOZQ-1; Thu, 05 Nov 2020 22:12:13 -0500 X-MC-Unique: Pf1tyOvTPw2ub-3Qr7YOZQ-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 539EE107B467; Fri, 6 Nov 2020 03:12:12 +0000 (UTC) Received: from x1.home (ovpn-112-213.phx2.redhat.com [10.3.112.213]) by smtp.corp.redhat.com (Postfix) with ESMTP id 877FA1C924; Fri, 6 Nov 2020 03:12:08 +0000 (UTC) Date: Thu, 5 Nov 2020 20:12:08 -0700 From: Alex Williamson To: Vikas Gupta Cc: Auger Eric , Cornelia Huck , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Vikram Prakash Subject: Re: [RFC, v0 1/3] vfio/platform: add support for msi Message-ID: <20201105201208.5366d71e@x1.home> In-Reply-To: References: <20201105060257.35269-1-vikas.gupta@broadcom.com> <20201105060257.35269-2-vikas.gupta@broadcom.com> <20201105000806.1df16656@x1.home> Organization: Red Hat MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 6 Nov 2020 08:24:26 +0530 Vikas Gupta wrote: > Hi Alex, > > On Thu, Nov 5, 2020 at 12:38 PM Alex Williamson > wrote: > > > > On Thu, 5 Nov 2020 11:32:55 +0530 > > Vikas Gupta wrote: > > > > > diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h > > > index 2f313a238a8f..aab051e8338d 100644 > > > --- a/include/uapi/linux/vfio.h > > > +++ b/include/uapi/linux/vfio.h > > > @@ -203,6 +203,7 @@ struct vfio_device_info { > > > #define VFIO_DEVICE_FLAGS_AP (1 << 5) /* vfio-ap device */ > > > #define VFIO_DEVICE_FLAGS_FSL_MC (1 << 6) /* vfio-fsl-mc device */ > > > #define VFIO_DEVICE_FLAGS_CAPS (1 << 7) /* Info supports caps */ > > > +#define VFIO_DEVICE_FLAGS_MSI (1 << 8) /* Device supports msi */ > > > __u32 num_regions; /* Max region index + 1 */ > > > __u32 num_irqs; /* Max IRQ index + 1 */ > > > __u32 cap_offset; /* Offset within info struct of first cap */ > > > > This doesn't make any sense to me, MSIs are just edge triggered > > interrupts to userspace, so why isn't this fully described via > > VFIO_DEVICE_GET_IRQ_INFO? If we do need something new to describe it, > > this seems incomplete, which indexes are MSI (IRQ_INFO can describe > > that)? We also already support MSI with vfio-pci, so a global flag for > > the device advertising this still seems wrong. Thanks, > > > > Alex > > > Since VFIO platform uses indexes for IRQ numbers so I think MSI(s) > cannot be described using indexes. That would be news for vfio-pci which has been describing MSIs with sub-indexes within indexes since vfio started. > In the patch set there is no difference between MSI and normal > interrupt for VFIO_DEVICE_GET_IRQ_INFO. Then what exactly is a global device flag indicating? Does it indicate all IRQs are MSI? > The patch set adds MSI(s), say as an extension, to the normal > interrupts and handled accordingly. So we have both "normal" IRQs and MSIs? How does the user know which indexes are which? > Do you see this is a violation? If Seems pretty unclear and dubious use of a global device flag. > yes, then we`ll think of other possible ways to support MSI for the > platform devices. > Macro VFIO_DEVICE_FLAGS_MSI can be changed to any other name if it > collides with an already supported vfio-pci or if not necessary, we > can remove this flag. If nothing else you're using a global flag to describe a platform device specific augmentation. We've recently added capabilities on the device info return that would be more appropriate for this, but fundamentally I don't understand why the irq info isn't sufficient. Thanks, Alex