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Y. Srinivasan" , Chris Oo , Ricardo Neri , linux-hyperv@vger.kernel.org, Haiyang Zhang , Krzysztof Kozlowski , linux-kernel@vger.kernel.org, "Ravi V. Shankar" , "Rafael J. Wysocki" , "Kirill A. Shutemov" , x86@kernel.org, Saurabh Sengar , Dexuan Cui , devicetree@vger.kernel.org Subject: Re: [PATCH v4 03/10] dt-bindings: reserved-memory: Wakeup Mailbox for Intel processors Message-ID: <20250604151720.GC29325@ranerica-svr.sc.intel.com> References: <20250603-rneri-wakeup-mailbox-v4-0-d533272b7232@linux.intel.com> <20250603-rneri-wakeup-mailbox-v4-3-d533272b7232@linux.intel.com> <174900070284.2624702.4580450009482590306.robh@kernel.org> 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: <174900070284.2624702.4580450009482590306.robh@kernel.org> User-Agent: Mutt/1.9.4 (2018-02-28) On Tue, Jun 03, 2025 at 08:31:42PM -0500, Rob Herring (Arm) wrote: > > On Tue, 03 Jun 2025 17:15:15 -0700, Ricardo Neri wrote: > > Add DeviceTree bindings to enumerate the wakeup mailbox used in platform > > firmware for Intel processors. > > > > x86 platforms commonly boot secondary CPUs using an INIT assert, de-assert > > followed by Start-Up IPI messages. The wakeup mailbox can be used when this > > mechanism is unavailable. > > > > The wakeup mailbox offers more control to the operating system to boot > > secondary CPUs than a spin-table. It allows the reuse of same wakeup vector > > for all CPUs while maintaining control over which CPUs to boot and when. > > While it is possible to achieve the same level of control using a spin- > > table, it would require to specify a separate `cpu-release-addr` for each > > secondary CPU. > > > > The operation and structure of the mailbox is described in the > > Multiprocessor Wakeup Structure defined in the ACPI specification. Note > > that this structure does not specify how to publish the mailbox to the > > operating system (ACPI-based platform firmware uses a separate table). No > > ACPI table is needed in DeviceTree-based firmware to enumerate the mailbox. > > > > Add a `compatible` property that the operating system can use to discover > > the mailbox. Nodes wanting to refer to the reserved memory usually define a > > `memory-region` property. /cpus/cpu* nodes would want to refer to the > > mailbox, but they do not have such property defined in the DeviceTree > > specification. Moreover, it would imply that there is a memory region per > > CPU. > > > > Co-developed-by: Yunhong Jiang > > Signed-off-by: Yunhong Jiang > > Signed-off-by: Ricardo Neri > > --- > > Changes since v3: > > - Removed redefinitions of the mailbox and instead referred to ACPI > > specification as per discussion on LKML. > > - Clarified that DeviceTree-based firmware do not require the use of > > ACPI tables to enumerate the mailbox. (Rob) > > - Described the need of using a `compatible` property. > > - Dropped the `alignment` property. (Krzysztof, Rafael) > > - Used a real address for the mailbox node. (Krzysztof) > > > > Changes since v2: > > - Implemented the mailbox as a reserved-memory node. Add to it a > > `compatible` property. (Krzysztof) > > - Explained the relationship between the mailbox and the `enable-mehod` > > property of the CPU nodes. > > - Expanded the documentation of the binding. > > > > Changes since v1: > > - Added more details to the description of the binding. > > - Added requirement a new requirement for cpu@N nodes to add an > > `enable-method`. > > --- > > .../reserved-memory/intel,wakeup-mailbox.yaml | 48 ++++++++++++++++++++++ > > 1 file changed, 48 insertions(+) > > > > My bot found errors running 'make dt_binding_check' on your patch: > > yamllint warnings/errors: > ./Documentation/devicetree/bindings/reserved-memory/intel,wakeup-mailbox.yaml:20:111: [warning] line too long (113 > 110 characters) (line-length) I did see this warning. I also see that none of the existing schema with links break them into multiple lines. Now I see that the yamllint configuration has allow-non-breakable-words: true I will put the link in separate line.