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[96.255.20.138]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-88d997aeef5sm20208696d6.27.2025.12.19.06.32.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 19 Dec 2025 06:32:09 -0800 (PST) Date: Fri, 19 Dec 2025 09:31:32 -0500 From: Gregory Price To: Jonathan Cameron Cc: linux-cxl@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, dave@stgolabs.net, dave.jiang@intel.com, alison.schofield@intel.com, vishal.l.verma@intel.com, ira.weiny@intel.com, dan.j.williams@intel.com, corbet@lwn.net Subject: Re: [PATCH v2] Documentation/driver-api/cxl: device hotplug section Message-ID: References: <20251218170747.1278327-1-gourry@gourry.net> <20251219105518.00005ca6@huawei.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251219105518.00005ca6@huawei.com> On Fri, Dec 19, 2025 at 10:55:18AM +0000, Jonathan Cameron wrote: > On Thu, 18 Dec 2025 12:07:47 -0500 > Gregory Price wrote: > > > + > > +Multi-Endpoint Memory Device Present at Boot > > +-------------------------------------------- > > +A hot-plug capable CXL memory device, such as one which presents multiple > > +expanders as a single large-capacity device, should report the maximum > > +*possible* capacity for the device at boot. :: > > + > > + HB0 > > + RP0 > > + | > > + [Multi-Endpoint Memory Device] > > So this is the weird switch as end point thing? Maybe a reference. > My guess is these will go away as switch and memory device vendors catch > up with the spec, but maybe I'm wrong. > I guess I just don't want to dictate the innards of a multi-endpoint memory device. It *really really* implies there must be some kind of switch inside - but that switch might not even be runtime programmable or discoverable (basically all the settings get locked on boot and it becomes passthrough). If you'd rather just not have this section at all, I'm ok with that. The switch case below this covers the base case for a switch-based device where everything is programmable. > > + _____|_____ > > + | | > > + [Endpoint0] [Empty] > > + > > + > > +Limiting the size to the capacity preset at boot will limit hot-add support > > +to replacing capacity that was present at boot. > >