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[96.255.20.138]) by smtp.gmail.com with ESMTPSA id af79cd13be357-8c6a724eadcsm12628385a.29.2026.01.15.10.56.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 15 Jan 2026 10:56:33 -0800 (PST) Date: Thu, 15 Jan 2026 13:56:01 -0500 From: Gregory Price To: Alejandro Lucero Palau Cc: linux-cxl@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, dave@stgolabs.net, jonathan.cameron@huawei.com, dave.jiang@intel.com, alison.schofield@intel.com, vishal.l.verma@intel.com, ira.weiny@intel.com, dan.j.williams@intel.com Subject: Re: [PATCH 0/6] CXL: Introduce memory controller abstraction and sysram controller Message-ID: References: <20260112163514.2551809-1-gourry@gourry.net> 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: On Thu, Jan 15, 2026 at 06:43:08PM +0000, Alejandro Lucero Palau wrote: > Hi Gregory, > > > I was concerned with how this could affect Type2 but I think there is no > issue at all, but I prefer to ask specifically about it. > > > Type2 can obtain an auto region if BIOS enabled/configured the HDMs, or it > can create one on purpose if not. Type2 patchset does not allow to create a > dax region when region probing and it will be the same type2 check > precluding call to enabling the sysram controller. > > > However, I can see the region will have default sysfs files for setting the > controller. I think even with such a change there is no way for enabling the > controller from the type2 region probing, so I guess it is safe, but I would > prefer to not allow a Type2 region setting a controller at all. > > > I like the approach for solving the problem pointed out, and I think > something similar or a controller extension for type2 could be needed in the > future, but maybe adding more flexibility for theoretical per type2 driver > memory-handling uniqueness. > > (pre-note: we changed the verbiage from controller to driver) I think Type2 devices (and some special memory devices) are exactly the use case that drives formalizing region-drivers. Some Type2 devices might just register a normal memory region. Some Type2 devices might want a dax device. Some Type2 devices might want a "private memory" region (private node). Some Type2 devices might have a completely different usage pattern. Maybe we might want a control that limits which drivers a given device can use (limiting switch-ability), and let devices inform the core region driver of that in some way. The sysfs toggle is a pressure-valve for devices that might be configurable in multiple ways. Maybe it won't actually be needed, but at least for "Regular Memory" devices i can see us having dax and sysram drivers at a minimum. The base sysram driver may even be the basis for a dcd_sysram driver. After all it's just a sysram driver w/ add/remove extent functions :] ~Gregory