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=-5.3 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 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 1392CC433E4 for ; Fri, 24 Jul 2020 23:46:53 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id D4454206E3 for ; Fri, 24 Jul 2020 23:46:52 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="e36Lin7T" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D4454206E3 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1jz7OZ-0007E7-2T; Fri, 24 Jul 2020 23:46:31 +0000 Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1jz7OX-0007E2-Cp for xen-devel@lists.xenproject.org; Fri, 24 Jul 2020 23:46:29 +0000 X-Inumbo-ID: e47cb61c-ce07-11ea-88ce-bc764e2007e4 Received: from mail.kernel.org (unknown [198.145.29.99]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id e47cb61c-ce07-11ea-88ce-bc764e2007e4; Fri, 24 Jul 2020 23:46:28 +0000 (UTC) Received: from localhost (c-67-164-102-47.hsd1.ca.comcast.net [67.164.102.47]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 84AFD206E3; Fri, 24 Jul 2020 23:46:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1595634387; bh=sFW7J/RkyNnfPfDMhsbVNhVbIhiIRPdKa0RlCygYldE=; h=Date:From:To:cc:Subject:In-Reply-To:References:From; b=e36Lin7TFrymDCxKw+eOLFZT6usDEqTFF0wEBo5mA/tZz8SswFRXHZTOJXR50r0bP GKoUyivPqFwlCPHKkKFRRdSzKOP6m1uwyrzj6VkPY4HZRN225PM3woxxXgiAZXFx5c wNerDdqJZVYqvydIOzB5l7x6zgcQKL1g+cCF0bKg= Date: Fri, 24 Jul 2020 16:46:27 -0700 (PDT) From: Stefano Stabellini X-X-Sender: sstabellini@sstabellini-ThinkPad-T480s To: Julien Grall Subject: Re: [RFC PATCH v1 1/4] arm/pci: PCI setup and PCI host bridge discovery within XEN on ARM. In-Reply-To: Message-ID: References: <64ebd4ef614b36a5844c52426a4a6a4a23b1f087.1595511416.git.rahul.singh@arm.com> <9f09ff42-a930-e4e3-d1c8-612ad03698ae@xen.org> <40582d63-49c7-4a51-b35b-8248dfa34b66@xen.org> User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: nd , Stefano Stabellini , Andrew Cooper , Bertrand Marquis , Jan Beulich , xen-devel , Rahul Singh , Volodymyr Babchuk , =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" On Fri, 24 Jul 2020, Julien Grall wrote: > On Fri, 24 Jul 2020 at 19:32, Stefano Stabellini wrote: > > > If they are not equal, then I fail to see why it would be useful to have this > > > value in Xen. > > > > I think that's because the domain is actually more convenient to use > > because a segment can span multiple PCI host bridges. So my > > understanding is that a segment alone is not sufficient to identify a > > host bridge. From a software implementation point of view it would be > > better to use domains. > > AFAICT, this would be a matter of one check vs two checks in Xen :). > But... looking at Linux, they will also use domain == segment for ACPI > (see [1]). So, I think, they still have to use (domain, bus) to do the lookup. > > > > In which case, we need to use PHYSDEVOP_pci_mmcfg_reserved so > > > Dom0 and Xen can synchronize on the segment number. > > > > I was hoping we could write down the assumption somewhere that for the > > cases we care about domain == segment, and error out if it is not the > > case. > > Given that we have only the domain in hand, how would you enforce that? > > >From this discussion, it also looks like there is a mismatch between the > implementation and the understanding on QEMU devel. So I am a bit > concerned that this is not stable and may change in future Linux version. > > IOW, we are know tying Xen to Linux. So could we implement > PHYSDEVOP_pci_mmcfg_reserved *or* introduce a new property that > really represent the segment? I don't think we are tying Xen to Linux. Rob has already said that linux,pci-domain is basically a generic device tree property. And if we look at https://www.devicetree.org/open-firmware/bindings/pci/pci2_1.pdf "PCI domain" is described and seems to match the Linux definition. I do think we need to understand the definitions and the differences. Reading online [1][2] it looks like a Linux PCI domain matches a "PCI Segment Group Number" in PCI Express which is probably why Linux is making the assumption that it is making. So maybe it is OK to use domains == segments, but we need to verify this in the specs and also clarify the terminology we use in a doc for our own sanity -- I am hoping that Rahul can come up with a good explanation on the topic :-) [1] https://stackoverflow.com/questions/49050847/how-is-pci-segmentdomain-related-to-multiple-host-bridgesor-root-bridges [2] https://wiki.osdev.org/PCI_Express