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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>
This commit is contained in:
Atish Patra 2022-04-20 19:48:56 -07:00 committed by Anup Patel
parent 9cd95e13bb
commit 4035ae94be
1 changed files with 31 additions and 18 deletions
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49
docs/pmu_support.md
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@ -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>;
};
```