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 Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id D5F01C83F2C for ; Tue, 5 Sep 2023 14:35:20 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qdX8q-0006jZ-Qz; Tue, 05 Sep 2023 10:34:57 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qdX8p-0006jN-0d; Tue, 05 Sep 2023 10:34:55 -0400 Received: from frasgout.his.huawei.com ([185.176.79.56]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qdX8m-0001er-AA; Tue, 05 Sep 2023 10:34:54 -0400 Received: from lhrpeml500005.china.huawei.com (unknown [172.18.147.200]) by frasgout.his.huawei.com (SkyGuard) with ESMTP id 4Rg7KC5D08z6HJ5h; Tue, 5 Sep 2023 22:33:19 +0800 (CST) Received: from localhost (10.122.247.231) by lhrpeml500005.china.huawei.com (7.191.163.240) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.31; Tue, 5 Sep 2023 15:34:39 +0100 Date: Tue, 5 Sep 2023 15:34:38 +0100 To: Yuquan Wang CC: qemu-arm , qemu-devel , gregory.price Subject: Re: CXL Namespaces of ACPI disappearing in Qemu demo Message-ID: <20230905153438.000075ff@huawei.com> In-Reply-To: <2023090518450211126476@phytium.com.cn> References: <2023082215220191352877@phytium.com.cn> <2023090518450211126476@phytium.com.cn> Organization: Huawei Technologies R&D (UK) Ltd. X-Mailer: Claws Mail 4.0.0 (GTK+ 3.24.29; x86_64-w64-mingw32) MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.122.247.231] X-ClientProxiedBy: lhrpeml100003.china.huawei.com (7.191.160.210) To lhrpeml500005.china.huawei.com (7.191.163.240) X-CFilter-Loop: Reflected Received-SPF: pass client-ip=185.176.79.56; envelope-from=jonathan.cameron@huawei.com; helo=frasgout.his.huawei.com X-Spam_score_int: -41 X-Spam_score: -4.2 X-Spam_bar: ---- X-Spam_report: (-4.2 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_MED=-2.3, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-to: Jonathan Cameron From: Jonathan Cameron via Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Tue, 5 Sep 2023 18:45:02 +0800 Yuquan Wang wrote: > Hi, Jonathan > On 2023-09-04 20:43, jonathan.cameron wrote: > > > > At the system design level, MMIO space of Root complex register space via RCRB > > does not map in a similar fashion to PCIE MMIO space (which is handled via > > address decoding in the PCIE fabric). It is much more similar to MMIO for platform > > devices - as such the implementation handles in like a platform device (well 16 of > > them which seemed enough for any sane usecase). > > > > > > Oh,thanks! According to above, therefore, the core factor is the implementation of RCRB. > > > > > So in theory we could make some space for the CXL root bridge RCRB registers > > but it would make various generic paths more complex. In a real system > > those registers are likely to be far from the PCI MMIO space anyway so the > > way it's modeled is probably more realistic than pushing the RCRB into the > > existing allocation. > > > > Here implies that all CXL root bridge will use RCRB registers. > > From Table 8-17 and Figure 9-14 in CXL3.0 specification, I understood that only RCH DP & > RCD UP will use RCRBs, and CXL host bridges VH mode will use other way to realize > the CHBCR. I had tried to find more explanation in CXL spec, but I haven't found. Hence > this is why I am confused. Ah. That distinction is a bit messy. Both an RCRB and CHBCR (CXL Host Bridge Component Registers) are similar in the sense that they are mapped in host memory space. As I understand it the distinction is more about the format / contents of that memory than how you access them. As an aside, they are described by a static ACPI table, so they can't be in the MMIO space used for BARs etc. Jonathan > > Many thanks > Yuquan