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 50745C38145 for ; Tue, 6 Sep 2022 08:54:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239067AbiIFIyG (ORCPT ); Tue, 6 Sep 2022 04:54:06 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49036 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239027AbiIFIxc (ORCPT ); Tue, 6 Sep 2022 04:53:32 -0400 Received: from frasgout.his.huawei.com (frasgout.his.huawei.com [185.176.79.56]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EDDF221B6; Tue, 6 Sep 2022 01:53:30 -0700 (PDT) Received: from fraeml713-chm.china.huawei.com (unknown [172.18.147.201]) by frasgout.his.huawei.com (SkyGuard) with ESMTP id 4MMK0G5sQNz687YW; Tue, 6 Sep 2022 16:52:46 +0800 (CST) Received: from lhrpeml500005.china.huawei.com (7.191.163.240) by fraeml713-chm.china.huawei.com (10.206.15.32) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.31; Tue, 6 Sep 2022 10:53:29 +0200 Received: from localhost (10.202.226.42) 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 15.1.2375.31; Tue, 6 Sep 2022 09:53:28 +0100 Date: Tue, 6 Sep 2022 09:53:27 +0100 From: Jonathan Cameron To: Robert Richter CC: Alison Schofield , Vishal Verma , Ira Weiny , Ben Widawsky , Dan Williams , , , Bjorn Helgaas , "Rafael J. Wysocki" , Len Brown Subject: Re: [PATCH 05/15] cxl/acpi: Add probe function to detect restricted CXL hosts in RCD mode Message-ID: <20220906095327.0000405b@huawei.com> In-Reply-To: References: <20220831081603.3415-1-rrichter@amd.com> <20220831081603.3415-6-rrichter@amd.com> <20220831110804.00003812@huawei.com> <20220901111038.00002e00@huawei.com> X-Mailer: Claws Mail 4.0.0 (GTK+ 3.24.29; i686-w64-mingw32) MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.202.226.42] X-ClientProxiedBy: lhrpeml100005.china.huawei.com (7.191.160.25) To lhrpeml500005.china.huawei.com (7.191.163.240) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 6 Sep 2022 09:19:49 +0200 Robert Richter wrote: > On 01.09.22 11:10:38, Jonathan Cameron wrote: > > On Thu, 1 Sep 2022 08:01:05 +0200 > > Robert Richter wrote: > > > On 31.08.22 11:08:04, Jonathan Cameron wrote: > > > > On Wed, 31 Aug 2022 10:15:53 +0200 > > > > Robert Richter wrote: > > > > > > The probe function is triggered by adding an own root device for RCHs. > > > > > This is different to CXL VH where an ACPI "ACPI0017" root device > > > > > exists. Its detection starts the CXL host detection. In RCD mode such > > > > > a device does not necessarily exists, so solve this by creating a > > > > > plain platform device that is not an ACPI device and is root only for > > > > > RCHs. > > > > > > > > If I read this correctly that platform device is created whether or not > > > > there are any cxl devices in the system? > > > > > > > > Can we create it only if we find some devices that will be placed > > > > under it later? > > > > > > This would move the host detection from probe to init which I wanted > > > to avoid to better control driver init order dependencies. > > > > It's a bit nasty either way. I can see your reasoning, but > > definitely not keen on it if there is a plausible way to avoid. > > > > > > I could add a put_device() at the end of a probe so that it will be > > > released in case no other references use it. This implies the refcount > > > is maintained for parent devices. Or this needs to be added to. So if > > > there are no children (hosts) attached to the root device after probe, > > > it will disappear. > > > > Unless there is precedence for that, it'll be weird enough to be > > hard to maintain. I guess I can live with the ugliness if we can't > > add something new to ACPI to base this off. > > Let's stay with a put_device() for now. Then, we wont have a stale cxl > root device in the system in case there are no RCD children. > > -Robert Kind of obvious, but... Make sure to call that out as an unusual thing to do via cover letter / patch description so we hopefully get more eyes on this detail.. Jonathan