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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C1174C38142 for ; Fri, 27 Jan 2023 10:01:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231755AbjA0KBy (ORCPT ); Fri, 27 Jan 2023 05:01:54 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41856 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231953AbjA0KBx (ORCPT ); Fri, 27 Jan 2023 05:01:53 -0500 Received: from frasgout.his.huawei.com (frasgout.his.huawei.com [185.176.79.56]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 222A727995 for ; Fri, 27 Jan 2023 02:01:52 -0800 (PST) Received: from lhrpeml500005.china.huawei.com (unknown [172.18.147.207]) by frasgout.his.huawei.com (SkyGuard) with ESMTP id 4P3Ch11Jfxz67kTG; Fri, 27 Jan 2023 17:58:25 +0800 (CST) Received: from localhost (10.202.227.76) 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 15.1.2375.34; Fri, 27 Jan 2023 10:01:49 +0000 Date: Fri, 27 Jan 2023 10:01:49 +0000 From: Jonathan Cameron To: Fan Ni CC: "qemu-devel@nongnu.org" , Michael Tsirkin , Ben Widawsky , "linux-cxl@vger.kernel.org" , "linuxarm@huawei.com" , Ira Weiny , Dave Jiang , "alison.schofield@intel.com" Subject: Re: [PATCH 2/2] hw/pxb-cxl: Support passthrough HDM Decoders unless overridden Message-ID: <20230127100149.0000563e@Huawei.com> In-Reply-To: <20230126215727.GA203951@bgt-140510-bm03> References: <20230125152703.9928-1-Jonathan.Cameron@huawei.com> <20230125152703.9928-3-Jonathan.Cameron@huawei.com> <20230126215727.GA203951@bgt-140510-bm03> Organization: Huawei Technologies Research and Development (UK) Ltd. X-Mailer: Claws Mail 4.1.0 (GTK 3.24.33; x86_64-w64-mingw32) MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.202.227.76] X-ClientProxiedBy: lhrpeml500003.china.huawei.com (7.191.162.67) To lhrpeml500005.china.huawei.com (7.191.163.240) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-cxl@vger.kernel.org On Thu, 26 Jan 2023 21:57:35 +0000 Fan Ni wrote: > On Wed, Jan 25, 2023 at 03:27:03PM +0000, Jonathan Cameron wrote: > > > The CXL r3.0 specification allows for there to be no HDM decoders on CXL > > Host Bridges if they have only a single root port. Instead, all accesses > > directed to the host bridge (as specified in CXL Fixed Memory Windows) > > are assumed to be routed to the single root port. > > > > Linux currently assumes this implementation choice. So to simplify testing, > > make QEMU emulation also default to no HDM decoders under these particular > > circumstances, but provide a hdm_for_passthrough boolean option to have > > HDM decoders as previously. > > > > Technically this is breaking backwards compatibility, but given the only > > known software stack used with the QEMU emulation is the Linux kernel > > and this configuration did not work before this change, there are > > unlikely to be any complaints that it now works. The option is retained > > to allow testing of software that does allow for these HDM decoders to exist, > > once someone writes it. > > > > Reported-by: Fan Ni > > Signed-off-by: Jonathan Cameron > > pxb_dev_realize_common(dev, CXL, errp); > > - pxb_dev_reset(DEVICE(dev)); > > + pxb_cxl_dev_reset(DEVICE(dev)); > > } > > > > +static Property pxb_cxl_dev_properties[] = { > > + /* Note: 0 is not a legal PXB bus number. */ > > + DEFINE_PROP_UINT8("bus_nr", PXBDev, bus_nr, 0), > > + DEFINE_PROP_UINT16("numa_node", PXBDev, numa_node, NUMA_NODE_UNASSIGNED), > > + DEFINE_PROP_BOOL("bypass_iommu", PXBDev, bypass_iommu, false), > > + DEFINE_PROP_BOOL("hdm_for_passthrough", PXBDev, hdm_for_passthrough, false), > when setting hdm_for_passthrough to true at the qemu command line, we > will see the segfault issue as before. I think this is expected as it > is the logic in cxl_cfmws_find_device. Wondering if there will be > following fixes to handle the case when hdm_for_passthrough is true. Absolutely, I'd expect a kernel fix for that case, but it's probably not high priority for anyone given we don't yet have any hardware that does that (as far as I know anyway!) I wanted to keep the control here to make that easy to test when we do have the fix in place. Jonathan