From: Abner Chang <renba.chang@...>

Initial description of PLIC  CLINT section of Linux-2022 platform.

On v6 commit,
  Remove the changes in Embedded-2022 section.

On v5 commit,
- Remove CLINT from platform spec
- Require ACLINT on Linux2020 platform and have a link to
https://github.com/riscv/riscv-aclint/blob/master/riscv-aclint.adoc.
- Remove Machine mode timer from previous patch because that is in the
scope of ACLINT
- For Embedded-2022 platform, mention Machine mode timer and refer to
ACLINT for the definition of registers

On v4 commit,
- PLIC section with [DEPRECATED] in Linux- 2022 chapter
- CLINT section in Linux- 2022 chapter for M-mode timer. We don't
mention
  IPI because AIA already supported it.
- In Embedded-2022 Machine mode timer section, CLINT is not mandatory.
- Separate section in appendix for the Machine mode timer registers

On v3 commit,
- Address review comments.

On v2 commit,
- CLINT is not deprecated.

- Add a standalone section for Machine Mode Timer in System
Peripherals.
  Do you think this is a good place for Machine Mode Timer?
  @Mayuresh, please check if you are ok with this change, not sure if
this
  overlaps with your text or not (The timer setion). I can remove this
  if you prefer to put this with your patch.

- In Embedded-2022, refer to Machine Mode Timer in System Peripherals
  section and CLINT in Linux-2022 Platform.
  @Alistair, is this ok?

On v1 commit,
- Not sure where to put the [DEPRECATED].
- Change the reference of PLIC in section 2.2.2. Interrupt Controller
to
  1.1.3.2 PLIC + CLINT section.

Signed-off-by: Abner Chang <renba.chang@...>
Cc: Alistair Francis <alistair.francis@...>
Cc: Sunil V L <sunilvl@...>
Cc: Mayuresh Chitale <mchitale@...>

---
 riscv-platform-spec.adoc | 25 ++++++++++++++++++++-----
 1 file changed, 20 insertions(+), 5 deletions(-)

diff --git a/riscv-platform-spec.adoc b/riscv-platform-spec.adoc
index 160c74a..c0ee75d 100644
--- a/riscv-platform-spec.adoc
+++ b/riscv-platform-spec.adoc
@@ -49,9 +49,24 @@ include::profiles.adoc[]
 * Start Address
 
 ==== Interrupt Controller
-* AIA
-* PLIC + CLINT
-* Interrupt Assignments
+===== AIA[[AIA]]
+===== PLIC[DEPRECATED][[PLIC]]
+The Platform Level Interrupt Controller (PLIC) provides facilities to
route
+the non-local interrupts to the external interrupt of a hart context
+with a given privilege mode in a given hart. The number of non-local
interrupt
+sources supported by PLIC and how does each of them connect to the
hart
+context is PLIC core implementation-specific. +
+(Refer to
https://github.com/riscv/riscv-plic-spec/blob/master/riscv-plic.adoc[RISC-V
 PLIC Specification]
+for the implementation reference of PLIC operation parameters)
+
+===== ACLINT
+Linux-2020 platform requires the Advanced Core Local Interruptor
(ACLINT,
+refer to
+
https://github.com/riscv/riscv-aclint/blob/master/riscv-aclint.adoc[RISC-V
 ACLINT Specification])
+to provide facilities to route inter-processor interrupt and Machine
mode timer
+interrupt to each RISC-V processor hart.
+
+===== Interrupt Assignments
 
 ==== System Peripherals
 * UART/Serial Console
@@ -289,8 +304,8 @@ Any RISC-V system that uses at least RV32/64G can
meet the Embedded-2022
 specification.
 
 ==== Interrupt Controller
-Embedded systems are recommended to use a spec compliant
-https://github.com/riscv/riscv-plic-spec[PLIC], a spec compliant
+Embedded systems are recommended to use a spec compliant
<<PLIC,PLIC>>,
+a spec compliant
 
https://github.com/riscv/riscv-fast-interrupt/blob/master/clic.adoc[CLIC]
 or both a CLIC and and PLIC.