diff options
Diffstat (limited to 'docs/specs/acpi_cpu_hotplug.txt')
| -rw-r--r-- | docs/specs/acpi_cpu_hotplug.txt | 51 |
1 files changed, 48 insertions, 3 deletions
diff --git a/docs/specs/acpi_cpu_hotplug.txt b/docs/specs/acpi_cpu_hotplug.txt index 9879f9ef7e..cb99cf3c8e 100644 --- a/docs/specs/acpi_cpu_hotplug.txt +++ b/docs/specs/acpi_cpu_hotplug.txt @@ -15,14 +15,14 @@ CPU present bitmap for: PIIX-PM (IO port 0xaf00-0xaf1f, 1-byte access) One bit per CPU. Bit position reflects corresponding CPU APIC ID. Read-only. The first DWORD in bitmap is used in write mode to switch from legacy - to new CPU hotplug interface, write 0 into it to do switch. + to modern CPU hotplug interface, write 0 into it to do switch. --------------------------------------------------------------- QEMU sets corresponding CPU bit on hot-add event and issues SCI with GPE.2 event set. CPU present map is read by ACPI BIOS GPE.2 handler to notify OS about CPU hot-add events. CPU hot-remove isn't supported. ===================================== -ACPI CPU hotplug interface registers: +Modern ACPI CPU hotplug interface registers: ------------------------------------- Register block base address: ICH9-LPC IO port 0x0cd8 @@ -67,6 +67,7 @@ write access: [0x0-0x3] CPU selector: (DWORD access) selects active CPU device. All following accesses to other registers will read/store data from/to selected CPU. + Valid values: [0 .. max_cpus) [0x4] CPU device control fields: (1 byte access) bits: 0: reserved, OSPM must clear it before writing to register. @@ -98,4 +99,48 @@ write access: 2: stores value into OST status register, triggers ACPI_DEVICE_OST QMP event from QEMU to external applications with current values of OST event and status registers. - other values: reserved + other values: reserved + +Typical usecases: + - (x86) Detecting and enabling modern CPU hotplug interface. + QEMU starts with legacy CPU hotplug interface enabled. Detecting and + switching to modern interface is based on the 2 legacy CPU hotplug features: + 1. Writes into CPU bitmap are ignored. + 2. CPU bitmap always has bit#0 set, corresponding to boot CPU. + + Use following steps to detect and enable modern CPU hotplug interface: + 1. Store 0x0 to the 'CPU selector' register, + attempting to switch to modern mode + 2. Store 0x0 to the 'CPU selector' register, + to ensure valid selector value + 3. Store 0x0 to the 'Command field' register, + 4. Read the 'Command data 2' register. + If read value is 0x0, the modern interface is enabled. + Otherwise legacy or no CPU hotplug interface available + + - Get a cpu with pending event + 1. Store 0x0 to the 'CPU selector' register. + 2. Store 0x0 to the 'Command field' register. + 3. Read the 'CPU device status fields' register. + 4. If both bit#1 and bit#2 are clear in the value read, there is no CPU + with a pending event and selected CPU remains unchanged. + 5. Otherwise, read the 'Command data' register. The value read is the + selector of the CPU with the pending event (which is already + selected). + + - Enumerate CPUs present/non present CPUs + 01. Set the present CPU count to 0. + 02. Set the iterator to 0. + 03. Store 0x0 to the 'CPU selector' register, to ensure that it's in + a valid state and that access to other registers won't be ignored. + 04. Store 0x0 to the 'Command field' register to make 'Command data' + register return 'CPU selector' value of selected CPU + 05. Read the 'CPU device status fields' register. + 06. If bit#0 is set, increment the present CPU count. + 07. Increment the iterator. + 08. Store the iterator to the 'CPU selector' register. + 09. Read the 'Command data' register. + 10. If the value read is not zero, goto 05. + 11. Otherwise store 0x0 to the 'CPU selector' register, to put it + into a valid state and exit. + The iterator at this point equals "max_cpus". |