| Virtual System Controller | |
| ========================= | |
| The ``virt-ctrl`` 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: | |
| 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). | |
| 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. |