[PATCH v2] dt-bindings: Add an enable method to RISC-V

[Palmer Dabbelt]

RISC-V doesn't currently specify a mechanism for enabling or disabling
CPUs.  Instead, we assume that all CPUs are enabled on boot, and if
someone wants to save power we instead put a CPU to sleep via a WFI
loop.  Future systems may have an explicit mechanism for putting a CPU
to sleep, so we're standardizing the device tree entry for when that
happens.

We're not defining a spin-table based interface to the firmware, as the
plan is to handle this entirely within the kernel instead.

CC: Mark Rutland <mark.rutland@xxxxxxx>
Signed-off-by: Palmer Dabbelt <palmer@xxxxxxxxxx>
---
 Documentation/devicetree/bindings/riscv/cpus.txt | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/Documentation/devicetree/bindings/riscv/cpus.txt b/Documentation/devicetree/bindings/riscv/cpus.txt
index adf7b7af5dc3..68f88eacc594 100644
--- a/Documentation/devicetree/bindings/riscv/cpus.txt
+++ b/Documentation/devicetree/bindings/riscv/cpus.txt
@@ -82,6 +82,15 @@ described below.
                 Value type: <string>
                 Definition: Contains the RISC-V ISA string of this hart.  These
                             ISA strings are defined by the RISC-V ISA manual.
+        - cpu-enable-method:
+                Usage: optional
+                Value type: <stringlist>
+                Definition: When absent, default is either "always-disabled"
+                            "always-enabled", depending on the current state
+                            of the CPU.
+                            Must be one of:
+                                * "always-disabled": This CPU cannot be enabled.
+                                * "always-enabled": This CPU cannot be disabled.
 
 Example: SiFive Freedom U540G Development Kit
 ---------------------------------------------
-- 
2.13.6