[PATCH] Documentation: riscv: note that counter access is part of the uABI

[Conor Dooley <conor.dooley@microchip.com>]

Commit 5a5294fbe020 ("RISC-V: Re-enable counter access from userspace")
fixed userspace access to CYCLE, TIME & INSTRET counters and left a nice
comment in-place about why they must not be restricted. Since we now
have a uABI doc in RISC-V land, add a section documenting it.

Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
---
Based on an, as yet, unsent v2 of my other uABI changes. I don't expect
it to be applicable, just getting a patch into patchwork while I don't
forget about this.
---
 Documentation/riscv/uabi.rst | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/Documentation/riscv/uabi.rst b/Documentation/riscv/uabi.rst
index 8d2651e42fda..638ddce56700 100644
--- a/Documentation/riscv/uabi.rst
+++ b/Documentation/riscv/uabi.rst
@@ -3,6 +3,13 @@
 RISC-V Linux User ABI
 =====================
 
+Counter access
+--------------
+
+Access to the CYCLE, TIME and INSTRET counters, now controlled by the SBI PMU
+extension, were part of the ISA when the uABI was frozen & so remain accessible
+from userspace.
+
 ISA string ordering in /proc/cpuinfo
 ------------------------------------
 

base-commit: 13ee7ef407cfcf63f4f047460ac5bb6ba5a3447d
prerequisite-patch-id: d17a9ffb6fcf99eb683728da98cd50e18cd28fe8
prerequisite-patch-id: 0df4127e3f4a0c02a235fea00bcb69cd94fabb38
prerequisite-patch-id: 171724b870ba212b714ebbded480269accd83733
-- 
2.38.1