skiboot: Add documentation for IMC opal call

Add documentation for new OPAL Call APIs added for
In Memory Collection(IMC) infrastructure. Three new
OPAL Call APIs are added and they are
	opal_imc_counters_init(int Domain, u64 address, u64 cpu_pir)
	opal_imc_counters_start(int Domain, u64 cpu_pir)
	opal_imc_counters_stop(int Domain, u64 cpu_pir)

Document details the input parameters and return values.

Acked-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Anju T Sudhakar <anju@linux.vnet.ibm.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.vnet.ibm.com>
Signed-off-by: Stewart Smith <stewart@linux.vnet.ibm.com>

doc/opal-api/opal-imc-counters.rst

@@ -0,0 +1,87 @@
+.. _opal-imc-counters:
+
+OPAL_IMC_COUNTERS_INIT
+==============================
+OPAL call interface to initialize In-memory collection
+infrastructure. Call does multiple scom writes on each
+incavation for Core IMC initialization. And for the
+Nest IMC, at this point, call is a no-op and returns
+OPAL_SUCCESS. Incase of kexec, OS driver should first
+stop the engine via OPAL_IMC_COUNTER_STOP(and then
+free the memory if allocated, for nest memory is
+mmapped). Incase of kdump, OS driver should stop
+the engine via OPAL_IMC_COUNTER_STOP.
+
+OPAL does sanity checks to detect unknown or
+unsupported IMC device type and nest units.
+check_imc_device_type() function removes
+unsupported IMC device type. disable_unavailable_units()
+removes unsupported nest units by the microcode.
+This way OPAL can lock down and advertise only
+supported device type and nest units.
+
+Parameters
+----------
+``uint32_t type``
+  This parameter specifies the imc counter domain.
+  The value should be 'OPAL_IMC_COUNTERS_CORE'
+
+``uint64_t addr``
+  This parameter must have a non-zero value.
+  This value must be a physical address of the core.
+
+``uint64_t cpu_pir``
+  This parameter specifices target cpu pir
+
+Returns
+-------
+OPAL_PARAMETER - In case of  unsupported ``type``
+OPAL_HARDWARE  - If any error in setting up the hardware.
+OPAL_SUCCESS   - On succesfully initialized or even if init operation is a no-op.
+
+
+OPAL_IMC_COUNTERS_START
+============================
+OPAL call interface for starting the In-Memory Collection
+counters for a specified domain (NEST/CORE).
+
+Parameters
+----------
+``uint32_t type``
+ This parameter specifies the imc counter domain.
+ The value can be either 'OPAL_IMC_COUNTERS_NEST'
+ or 'OPAL_IMC_COUNTERS_CORE'
+
+``uint64_t cpu_pir``
+  This parameter specifices target cpu pir
+
+Returns
+-------
+OPAL_PARAMETER - In case of  Unsupported ``type``
+OPAL_HARDWARE  - If any error in setting up the hardware.
+OPAL_SUCCESS   - On successful execution of the operation for the given ``type``.
+
+
+OPAL_IMC_COUNTERS_STOP
+===========================
+OPAL call interface for stoping In-Memory
+Collection counters for a specified domain (NEST/CORE).
+STOP should always be called after a related START.
+While STOP *may* run successfully without an associated
+START call, this is not gaurenteed.
+
+Parameters
+----------
+``uint32_t type``
+ This parameter specifies the imc counter domain.
+ The value can be either 'OPAL_IMC_COUNTERS_NEST'
+ or 'OPAL_IMC_COUNTERS_CORE'
+
+``uint64_t cpu_pir``
+  This parameter specifices target cpu pir
+
+Returns
+-------
+OPAL_PARAMETER - In case of  Unsupported ``type``
+OPAL_HARDWARE  - If any error in setting up the hardware.
+OPAL_SUCCESS   - On successful execution of the operation for the given ``type``.