From cf9610f9116d55c5a66ef9f1faecacabd93a9322 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Mon, 24 Aug 2026 08:46:03 -0700 Subject: Merge tag 'pinctrl-v7.3-1' of git://git.kernel.org/pub/scm/linux/kernel/git/linusw/linux-pinctrl Pull pin control updates from Linus Walleij: "Core changes: - Use the non-blocking mux_state_try_select() in the generic MUX pin control back-end - Free pin maps on pinctrl_generic_to_map() failure in the core helpers New hardware pin control: - Qualcomm Maili TLMM SoC, PMG1110 PMIC, and Eliza LPASS LPI TLMM SoC (this is for the low power audio, LPASS = Low Power Audio SubSystem portions) - Upboard support on top of the Intel pin controller - Apple T6030 and T6031 support (just compatible strings) - Samsung Exynos 8855 SoC - Mediatek MT6858 SoC - Rockchip RK3308B and RV1106 SoCs - Airoha EN7523 and AN7563 SoCs Improvements: - Qualcomm TLMM GPIOs are unconditionally marked as wakeup capable - Qualcomm improvements on top of the Qualcomm PDC (power domain controller) irqchip improvements from tglx:s tree - Qualcomm IPQ806x and IPQ9650 non-urgent pin grop fixups - The NPCM8xx driver has been put into shape fixing many pin and group definitions - Some non-urgent Tegra 264 pin assignments are fixed up - Some non-urgent fixups to Airoha AN7581 and AN7583 registers and pin assignments, missing features etc" * tag 'pinctrl-v7.3-1' of git://git.kernel.org/pub/scm/linux/kernel/git/linusw/linux-pinctrl: (130 commits) dt-bindings: pinctrl: Convert TI DA850 pupd to DT schema pinctrl: meson: sync some modify from A4 pinctrl: meson: a4: Add input enable pin configuration pinctrl: realtek: rtd1625: remove unused group name spdif_sel pinctrl: realtek: rtd1625: fix base_bit for VE4 GPIO 13 dt-bindings: pinctrl: microchip,pic32mzda-pinctrl: Convert to DT schema Revert "Merge branch 'ib-rsk7204' into devel" pinctrl: rockchip: Add RV1106 pinctrl support dt-bindings: pinctrl: rockchip: Add RV1106 compatible pinctrl: rockchip: Decode drive strength in the get function pinctrl: fix PINCTRL_GENERIC_MUX not always being selectable pinctrl: airoha: add support of an7563 SoC dt-bindings: pinctrl: airoha: add support of an7563 pin controller pinctrl: airoha: try to find chip scu node by phandle first pinctrl: airoha: add support of en7523 SoC dt-bindings: pinctrl: airoha: add support of en7523 pin controller pinctrl: airoha: an7583: add support for olt pinmux pinctrl: airoha: an7583: add support for pon_alt pinmux pinctrl: airoha: an7583: add support for npu_uart pinmux dt-bindings: pinctrl: airoha: an7583: add missed features ... --- Documentation/arch/arm64/cpu-hotplug.rst | 83 ++++++++++++++++++++++++++++++++ 1 file changed, 83 insertions(+) create mode 100644 Documentation/arch/arm64/cpu-hotplug.rst (limited to 'Documentation/arch/arm64/cpu-hotplug.rst') diff --git a/Documentation/arch/arm64/cpu-hotplug.rst b/Documentation/arch/arm64/cpu-hotplug.rst new file mode 100644 index 000000000..7c3379b70 --- /dev/null +++ b/Documentation/arch/arm64/cpu-hotplug.rst @@ -0,0 +1,83 @@ +.. SPDX-License-Identifier: GPL-2.0 +.. _cpuhp_index: + +==================== +CPU Hotplug and ACPI +==================== + +CPU hotplug in the arm64 world is commonly used to describe the kernel taking +CPUs online/offline using PSCI. This document is about ACPI firmware allowing +CPUs that were not available during boot to be added to the system later. + +``possible`` and ``present`` refer to the state of the CPU as seen by linux. + + +CPU Hotplug on physical systems - CPUs not present at boot +---------------------------------------------------------- + +Physical systems need to mark a CPU that is ``possible`` but not ``present`` as +being ``present``. An example would be a dual socket machine, where the package +in one of the sockets can be replaced while the system is running. + +This is not supported. + +In the arm64 world CPUs are not a single device but a slice of the system. +There are no systems that support the physical addition (or removal) of CPUs +while the system is running, and ACPI is not able to sufficiently describe +them. + +e.g. New CPUs come with new caches, but the platform's cache topology is +described in a static table, the PPTT. How caches are shared between CPUs is +not discoverable, and must be described by firmware. + +e.g. The GIC redistributor for each CPU must be accessed by the driver during +boot to discover the system wide supported features. ACPI's MADT GICC +structures can describe a redistributor associated with a disabled CPU, but +can't describe whether the redistributor is accessible, only that it is not +'always on'. + +arm64's ACPI tables assume that everything described is ``present``. + + +CPU Hotplug on virtual systems - CPUs not enabled at boot +--------------------------------------------------------- + +Virtual systems have the advantage that all the properties the system will +ever have can be described at boot. There are no power-domain considerations +as such devices are emulated. + +CPU Hotplug on virtual systems is supported. It is distinct from physical +CPU Hotplug as all vCPU resources are statically described in the firmware +configuration tables (e.g. MADT), meaning their maximum possible count is +known at boot. However, vCPUs that are not enabled at boot are not marked +as ``present`` by the kernel until they are hotplugged. An example is where +a virtual machine boots with a single CPU, and additional CPUs are added +once a cloud orchestrator deploys the workload. + +For a virtual machine, the VMM (e.g. Qemu) plays the part of firmware. + +Virtual hotplug is implemented as a firmware policy affecting which CPUs can be +brought online. Firmware can enforce its policy via PSCI's return codes. e.g. +``DENIED``. + +The ACPI tables must describe all the resources of the virtual machine. CPUs +that are hot-pluggable must have the ``online capable`` bit set and the +``enabled`` bit cleared in the MADT GICC structures to indicate they can be +enabled later. The boot CPU must be marked as ``enabled`` with its +``online capable`` bit cleared. The 'always on' GICR structure must be used +to describe the redistributors. + +CPUs described as ``online capable`` but not ``enabled`` can be set to enabled +by the DSDT's Processor object's _STA method. On virtual systems the _STA method +must always set the ``ACPI_STA_DEVICE_PRESENT`` bit, while toggling the +``ACPI_STA_DEVICE_ENABLED`` bit to reflect its plug status. The kernel will +then dynamically mark the vCPU as ``present`` within the OS when the +``ACPI_STA_DEVICE_ENABLED`` bit becomes set during hot-add. Changes to the +firmware policy can be notified to the OS via device-check or eject-request. + +CPUs described as ``enabled`` in the static table, should not have their _STA +modified dynamically by firmware. Soft-restart features such as kexec will +re-read the static properties of the system from these static tables, and +may malfunction if these no longer describe the running system. Linux will +re-discover the dynamic properties of the system from the _STA method later +during boot. -- cgit v1.3.1