Clarify values of "CPU selector' register and add workflows for
* finding CPU with pending 'insert/remove' event
* enumerating present/non present CPUs
Signed-off-by: Igor Mammedov <imamm...@redhat.com>
---
docs/specs/acpi_cpu_hotplug.txt | 22 ++++++++++++++++++++++
1 file changed, 22 insertions(+)
diff --git a/docs/specs/acpi_cpu_hotplug.txt b/docs/specs/acpi_cpu_hotplug.txt
index ac5903b2b1..43c5a193f0 100644
--- a/docs/specs/acpi_cpu_hotplug.txt
+++ b/docs/specs/acpi_cpu_hotplug.txt
@@ -54,6 +54,7 @@ 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.
@@ -93,3 +94,24 @@ Selecting CPU device beyond possible range has no effect on
platform:
ignored
- read accesses to CPU hot-plug registers not documented above return
all bits set to 0.
+
+Typical usecases:
+ - Get a cpu with pending event
+ 1. write 0x0 into 'Command field' register
+ 2. read from 'Command data' register, CPU selector value (CPU's UID in
ACPI
+ tables) and event for selected CPU from 'CPU device status fields'
+ register. If there aren't pending events, CPU selector value doesn't
+ change and 'insert' and 'remove' bits are not set.
+ - Enumerate CPUs present/non present CPUs.
+ 1. set iterator to 0x0
+ 2. write 0x0 into 'Command field' register and then iterator
+ into 'CPU selector' register.
+ 3. read 'enabled' flag for selected CPU from 'CPU device status fields'
+ register
+ 4. to continue to the next CPU, increment iterator and repeat step 2
+ 5. read 'Command data' register
+ 5.1 if 'Command data' register matches iterator continue to step 3.
+ (read presence bit for the next CPU)
+ 5.2 if 'Command data' register has not changed, there is not CPU
+ corresponding to iterator value and the last valid iterator value
+ equals to 'max_cpus' + 1
--
2.18.1
