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Wysocki" Cc: x86@kernel.org, Krzysztof Kozlowski , Conor Dooley , Rob Herring , "K. Y. Srinivasan" , Haiyang Zhang , Wei Liu , Dexuan Cui , Michael Kelley , devicetree@vger.kernel.org, Saurabh Sengar , Chris Oo , linux-hyperv@vger.kernel.org, "Kirill A. Shutemov" , linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org, "Ravi V. Shankar" , Ricardo Neri Subject: Re: [PATCH v3 03/13] x86/acpi: Move acpi_wakeup_cpu() and helpers to smpboot.c Message-ID: <20250506053726.GF25533@ranerica-svr.sc.intel.com> References: <20250503191515.24041-1-ricardo.neri-calderon@linux.intel.com> <20250503191515.24041-4-ricardo.neri-calderon@linux.intel.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=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) On Mon, May 05, 2025 at 12:03:13PM +0200, Rafael J. Wysocki wrote: > On Sat, May 3, 2025 at 9:10 PM Ricardo Neri > wrote: > > > > The bootstrap processor uses acpi_wakeup_cpu() to indicate to firmware that > > it wants to boot a secondary CPU using a mailbox as described in the > > Multiprocessor Wakeup Structure of the ACPI specification. > > > > The wakeup mailbox does not strictly require support from ACPI. > > Well, except that it is defined by the ACPI specification. That is true. > > > The platform firmware can implement a mailbox compatible in structure and > > operation and enumerate it using other mechanisms such a DeviceTree graph. > > So is there a specification defining this mechanism? > > It is generally not sufficient to put the code and DT bindings > unilaterally into the OS and expect the firmware to follow suit. > This mechanism is described in the section 4.3.5 of the Intel TDX Virtual Firmware Design Guide [1], but it refeers to the ACPI specification for the interface. > > Move the code used to setup and use the mailbox out of the ACPI > > directory to use it when support for ACPI is not available or needed. > > I think that the code implementing interfaces defined by the ACPI > specification is not generic and so it should not be built when the > kernel is configured without ACPI support. Support for ACPI would not be used on systems describing hardware using a DeviceTree graph. My goal is to have a common interface that both DT and ACPI can use. I think what is missing is that common interface. Would it be preferred to have a separate implementation that is functionally equivalent? Thanks and BR, Ricardo [1]. https://cdrdv2-public.intel.com/733585/tdx-virtual-firmware-design-guide-rev-004-20231206.pdf