docs: pmu: Improve the PMU DT bindings

The current DT binding description is misleading and confusing. Clarify
the text and provide more examples.

Signed-off-by: Atish Patra <atishp@rivosinc.com>
Reviewed-by: Anup Patel <anup@brainfault.org>

1 files changed, 31 insertions, 18 deletions

diff --git a/docs/pmu_support.md b/docs/pmu_support.md
index 7e3367c..8751bb5 100644
--- a/docs/pmu_support.md
+++ b/docs/pmu_support.md
@@ -51,37 +51,50 @@ shouldn't encode any raw event.
 
 * **riscv,raw-event-to-mhpmcounters**(Optional) - It represents an ONE-to-MANY
 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).
+a bitmap format that can be used to monitor that raw event. The encoding of the
+raw events are platform specific. The information is encoded in a table format
+where each row represent the specific raw event(s). The first column is a 64bit
+match value where the invariant bits of range of events are set. The second
+column is a 64 bit mask that will have all the variant bits of the range of
+events cleared. Every other bits should be set in the mask.
+The third column is a 32bit value to represent bitmap of all MHPMCOUNTERx that
+can monitor these set of event(s).
+If a platform directly encodes each raw PMU event as a unique ID, the value of
+select_mask must be 0xffffffff_ffffffff.
 
 *Note:* A platform may choose to provide the mapping between event & counters
 via platform hooks rather than the device tree.
 
-### Example
+### Example 1
 
 ```
 pmu {
 	compatible 			= "riscv,pmu";
-	interrupts 			= <0x100>;
-	interrupt-parent 			= <&plic>
 	riscv,event-to-mhpmevent 		= <0x0000B  0x0000 0x0001>,
 	riscv,event-to-mhpmcounters 	= <0x00001 0x00001 0x00000001>,
 						  <0x00002 0x00002 0x00000004>,
 						  <0x00003 0x0000A 0x00000ff8>,
 						  <0x10000 0x10033 0x000ff000>,
-	riscv,raw-event-to-mhpmcounters = <0x0000     0x0002 0xffffffff 0xffffffff 0x00000f8>,
-					  <0xffffffff 0xfffffff0 0xffffffff 0xfffffff0 0x00000ff0>,
+					/* For event ID 0x0002 */
+	riscv,raw-event-to-mhpmcounters = <0x0000 0x0002 0xffffffff 0xffffffff 0x00000f8>,
+					/* For event ID 0-4 */
+					<0x0 0x0 0xffffffff 0xfffffff0 0x00000ff0>,
+					/* For event ID 0xffffffff0000000f - 0xffffffff000000ff */
+					<0xffffffff 0x0 0xffffffff 0xffffff0f 0x00000ff0>,
 };
+```
+
+### Example 2
 
 ```
+/*
+ * For HiFive Unmatched board. The encodings can be found here
+ * https://sifive.cdn.prismic.io/sifive/1a82e600-1f93-4f41-b2d8-86ed8b16acba_fu740-c000-manual-v1p6.pdf
+ */
+pmu {
+	compatible 			= "riscv,pmu";
+	riscv,raw-event-to-mhpmcounters = <0x0 0x0 0xffffffff 0xfc0000ff 0xc>,
+					  <0x0 0x1 0xffffffff 0xfff800ff 0xc>,
+					  <0x0 0x2 0xffffffff 0xffffe0ff 0xc>;
+};
+```