m68k: add a system controller

Add a system controller for the m68k-virt machine.
This controller allows the kernel to power off or reset the machine.

Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Tested-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20210312214145.2936082-5-laurent@vivier.eu>

1 files changed, 26 insertions, 0 deletions

diff --git a/docs/specs/virt-ctlr.txt b/docs/specs/virt-ctlr.txt
new file mode 100644
index 0000000000..24d38084f7
--- /dev/null
+++ b/docs/specs/virt-ctlr.txt
@@ -0,0 +1,26 @@
+Virtual System Controller
+=========================
+
+This device is a simple interface defined for the pure virtual machine with no
+hardware reference implementation to allow the guest kernel to send command
+to the host hypervisor.
+
+The specification can evolve, the current state is defined as below.
+
+This is a MMIO mapped device using 256 bytes.
+
+Two 32bit registers are defined:
+
+1- the features register (read-only, address 0x00)
+
+   This register allows the device to report features supported by the
+   controller.
+   The only feature supported for the moment is power control (0x01).
+
+2- the command register (write-only, address 0x04)
+
+   This register allows the kernel to send the commands to the hypervisor.
+   The implemented commands are part of the power control feature and
+   are reset (1), halt (2) and panic (3).
+   A basic command, no-op (0), is always present and can be used to test the
+   register access. This command has no effect.