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=-8.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham 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 C3FE9C4320A for ; Fri, 20 Aug 2021 14:35:01 +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 88D69610FF for ; Fri, 20 Aug 2021 14:35:01 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 88D69610FF Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=xen.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=lists.xenproject.org Received: from list by lists.xenproject.org with outflank-mailman.169560.309745 (Exim 4.92) (envelope-from ) id 1mH5ba-0006my-Sj; Fri, 20 Aug 2021 14:34:46 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 169560.309745; Fri, 20 Aug 2021 14:34:46 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1mH5ba-0006mr-Pp; Fri, 20 Aug 2021 14:34:46 +0000 Received: by outflank-mailman (input) for mailman id 169560; Fri, 20 Aug 2021 14:34:45 +0000 Received: from mail.xenproject.org ([104.130.215.37]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1mH5bZ-0006ml-Hc for xen-devel@lists.xenproject.org; Fri, 20 Aug 2021 14:34:45 +0000 Received: from xenbits.xenproject.org ([104.239.192.120]) by mail.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1mH5bY-0004JY-GB; Fri, 20 Aug 2021 14:34:44 +0000 Received: from [54.239.6.185] (helo=a483e7b01a66.ant.amazon.com) by xenbits.xenproject.org with esmtpsa (TLS1.3:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.92) (envelope-from ) id 1mH5bY-0003Sh-9N; Fri, 20 Aug 2021 14:34:44 +0000 X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=xen.org; s=20200302mail; h=Content-Transfer-Encoding:Content-Type:In-Reply-To: MIME-Version:Date:Message-ID:From:References:Cc:To:Subject; bh=cF04O8AFn9oyP+EjTMf7BULsEC/mKak+muIdJIm4AA4=; b=ukkyumCVB0R1muBi74T1EnOiEX Atgw3Pz5J4/AUIVFuKTaY8bWL3W3deS8g2IGC5JHkMYXvFOyC9D/oJ0Hip9nHY/IFYy2x0PTEDzOy DIEYA/+YrgiE+v0iOhchmZibX4bGRQWuNS3iW6PQH8kiLAQ3Ihz/Z3j2pwWVJtaWKFcE=; Subject: Re: [PATCH v1 09/14] xen/arm: Add cmdline boot option "pci=on" To: Rahul Singh Cc: xen-devel , Bertrand Marquis , Stefano Stabellini , Volodymyr Babchuk References: <731afb80-bb68-0c66-4f0f-341a46118770@xen.org> From: Julien Grall Message-ID: Date: Fri, 20 Aug 2021 15:34:42 +0100 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit On 20/08/2021 13:19, Rahul Singh wrote: > Hi Julien, Hi Rahul, > >> On 19 Aug 2021, at 1:31 pm, Julien Grall wrote: >> >> Hi Rahul, >> >> On 19/08/2021 13:02, Rahul Singh wrote: >>> Add cmdline boot option "pci=on" to enable/disable the PCI init during >>> boot. >> >> I read this as "PCI" will be either disabled/enabled for the platform. Whereas, I think it will be used to decide whether Xen discover PCI and PCI passthrough is supported or not. > > Yes. I will modify the option to "pci-passthrough== " >> >> Can you also clarify why a user would want to select "pci=off"? > > As pci-passthrough support emulate the PCI devices for DOM0 also, I thought if someone want to > boot the DOM0 without emulating the PCI device in XEN and wants to have direct access to device. Dom0 will always have direct access to the PCI device. The only difference is whether the access to the hostbridge and config space will be trapped by Xen. I expect the both to mainly happen during boot and therefore the overhead will be limited. > > I am ok to drop this patch if you feel adding the option is not required at all. One of the reason I could see this option to be useful is to figure out if an issue occurs because of the hostbridge emulation. Yet, I am still not fully convinced adding an option is worth it. Jan and others, any opinions? Cheers, -- Julien Grall