lib: pmu: support the event ID encoded by a bitmap.

RISC-V privilege specification does not specify how to encode the event ID.
Therefore, each platform is allowed to customize its own encoding rule.
The common encoding methods are as follow, directly assigning a number to an
event, or every bit in the mphmevent CSR controls one specified event or
mixes the above two methods.

To enable OpenSBI to support the above three encoding methods simultaneously,
this patch repurpose the dt property "riscv,raw-event-to-mhpmcounters". The
"riscv,raw-event-to-mhpmcounters" will describes the one or multiple raw
events that could be counted by a set of counters. But, the column number
of "riscv,raw-event-to-mhpmcounters" is extended from 2 to 3. The 1st column
(64bit) is the ID of the raw events. The 2nd column (64bit) represents a
select_mask now to represent the bits used for event ID encoding.
If a platform directly encodes each raw PMU event as a unique ID,
the value of select_mask will be 0xffffffff_ffffffff.

Signed-off-by: Vincent Chen <vincent.chen@sifive.com>
Signed-off-by: Atish Patra<atishp@rivosinc.com>
Reviewed-by: Anup Patel <anup.patel@wdc.com>

1 files changed, 16 insertions, 8 deletions

diff --git a/docs/pmu_support.md b/docs/pmu_support.md
index a60b75c..7e3367c 100644
--- a/docs/pmu_support.md
+++ b/docs/pmu_support.md
@@ -50,12 +50,20 @@ event-to-mhpmevent is present. Otherwise, it can be omitted. This property
 shouldn't encode any raw event.
 
 * **riscv,raw-event-to-mhpmcounters**(Optional) - It represents an ONE-to-MANY
-mapping between a raw event and all the MHPMCOUNTERx in a bitmap format that can
-be used to monitor that raw event. The information is encoded in a table format
-where each raw represent a specific raw event. The first column stores the
-expected event selector value that should be encoded in the expected value to be
-written in MHPMEVENTx. The second column stores a bitmap of all the MHPMCOUNTERx
-that can be used for monitoring the specified event.
+or MANY-to-MANY mapping between the raw event(s) and all the MHPMCOUNTERx in
+a bitmap format that can be used to monitor that raw event, which depends on
+how the platform encodes the monitor events. Currently, only the following three
+encoding methods are supported, encoding each event as a number, using a bitmap
+to encode monitor events, and mixing the previous two methods. The information
+is encoded in a table format where each row represent the specific raw event(s).
+The first column represents a 64-bit selector value which can indicate an
+monitor event ID (encoded by a number) or an event set (encoded by a bitmap).
+In case of the latter, the lower bits used to encode a set of events should be
+set to zero. The second column is a 64-bit selector mask where any bits used
+for event encoding will be cleared. If a platform directly encodes each raw PMU
+event as a unique ID, the value of select_mask will be 0xffffffff_ffffffff.
+The third column represent a bitmap of all the MHPMCOUNTERx that can be used for
+monitoring the specified event(s).
 
 *Note:* A platform may choose to provide the mapping between event & counters
 via platform hooks rather than the device tree.
@@ -72,8 +80,8 @@ pmu {
 						  <0x00002 0x00002 0x00000004>,
 						  <0x00003 0x0000A 0x00000ff8>,
 						  <0x10000 0x10033 0x000ff000>,
-	riscv,raw-event-to-mhpmcounters 	= <0x0000 0x0002 0x00000f8>,
-					  <0x0000 0x0003 0x00000ff0>,
+	riscv,raw-event-to-mhpmcounters = <0x0000     0x0002 0xffffffff 0xffffffff 0x00000f8>,
+					  <0xffffffff 0xfffffff0 0xffffffff 0xfffffff0 0x00000ff0>,
 };
 
 ```