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Diffstat (limited to 'docs/specs/acpi_mem_hotplug.rst')
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diff --git a/docs/specs/acpi_mem_hotplug.rst b/docs/specs/acpi_mem_hotplug.rst new file mode 100644 index 0000000000..069819bc3e --- /dev/null +++ b/docs/specs/acpi_mem_hotplug.rst @@ -0,0 +1,128 @@ +QEMU<->ACPI BIOS memory hotplug interface +========================================= + +ACPI BIOS GPE.3 handler is dedicated for notifying OS about memory hot-add +and hot-remove events. + +Memory hot-plug interface (IO port 0xa00-0xa17, 1-4 byte access) +---------------------------------------------------------------- + +Read access behavior +^^^^^^^^^^^^^^^^^^^^ + +[0x0-0x3] + Lo part of memory device phys address +[0x4-0x7] + Hi part of memory device phys address +[0x8-0xb] + Lo part of memory device size in bytes +[0xc-0xf] + Hi part of memory device size in bytes +[0x10-0x13] + Memory device proximity domain +[0x14] + Memory device status fields + + bits: + + 0: + Device is enabled and may be used by guest + 1: + Device insert event, used to distinguish device for which + no device check event to OSPM was issued. + It's valid only when bit 1 is set. + 2: + Device remove event, used to distinguish device for which + no device eject request to OSPM was issued. + 3-7: + reserved and should be ignored by OSPM + +[0x15-0x17] + reserved + +Write access behavior +^^^^^^^^^^^^^^^^^^^^^ + + +[0x0-0x3] + Memory device slot selector, selects active memory device. + All following accesses to other registers in 0xa00-0xa17 + region will read/store data from/to selected memory device. +[0x4-0x7] + OST event code reported by OSPM +[0x8-0xb] + OST status code reported by OSPM +[0xc-0x13] + reserved, writes into it are ignored +[0x14] + Memory device control fields + + bits: + + 0: + reserved, OSPM must clear it before writing to register. + Due to BUG in versions prior 2.4 that field isn't cleared + when other fields are written. Keep it reserved and don't + try to reuse it. + 1: + if set to 1 clears device insert event, set by OSPM + after it has emitted device check event for the + selected memory device + 2: + if set to 1 clears device remove event, set by OSPM + after it has emitted device eject request for the + selected memory device + 3: + if set to 1 initiates device eject, set by OSPM when it + triggers memory device removal and calls _EJ0 method + 4-7: + reserved, OSPM must clear them before writing to register + +Selecting memory device slot beyond present range has no effect on platform: + +- write accesses to memory hot-plug registers not documented above are ignored +- read accesses to memory hot-plug registers not documented above return + all bits set to 1. + +Memory hot remove process diagram +--------------------------------- + +:: + + +-------------+ +-----------------------+ +------------------+ + | 1. QEMU | | 2. QEMU | |3. QEMU | + | device_del +---->+ device unplug request +----->+Send SCI to guest,| + | | | cb | |return control to | + | | | | |management | + +-------------+ +-----------------------+ +------------------+ + + +---------------------------------------------------------------------+ + + +---------------------+ +-------------------------+ + | OSPM: | remove event | OSPM: | + | send Eject Request, | | Scan memory devices | + | clear remove event +<-------------+ for event flags | + | | | | + +---------------------+ +-------------------------+ + | + | + +---------v--------+ +-----------------------+ + | Guest OS: | success | OSPM: | + | process Ejection +----------->+ Execute _EJ0 method, | + | request | | set eject bit in flags| + +------------------+ +-----------------------+ + |failure | + v v + +------------------------+ +-----------------------+ + | OSPM: | | QEMU: | + | set OST event & status | | call device unplug cb | + | fields | | | + +------------------------+ +-----------------------+ + | | + v v + +------------------+ +-------------------+ + |QEMU: | |QEMU: | + |Send OST QMP event| |Send device deleted| + | | |QMP event | + +------------------+ | | + +-------------------+ |