acpi: cpuhp: introduce 'Command data 2' field

No functional change in practice, patch only aims to properly
document (in spec and code) intended usage of the reserved space.

The new field is to be used for 2 purposes:
  - detection of modern CPU hotplug interface using
    CPHP_GET_NEXT_CPU_WITH_EVENT_CMD command.
    procedure will be described in follow up patch:
      "acpi: cpuhp: spec: add typical usecases"
  - for returning upper 32 bits of architecture specific CPU ID,
    for new CPHP_GET_CPU_ID_CMD command added by follow up patch:
      "acpi: cpuhp: add CPHP_GET_CPU_ID_CMD command"

Change is backward compatible with 4.2 and older machines, as field was
unconditionally reserved and always returned 0x0 if modern CPU hotplug
interface was enabled.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Message-Id: <1575896942-331151-8-git-send-email-imammedo@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/hw/acpi/cpu.c b/hw/acpi/cpu.c
index 87f30a31d7..d475c06953 100644
--- a/hw/acpi/cpu.c
+++ b/hw/acpi/cpu.c
@@ -12,6 +12,7 @@
 #define ACPI_CPU_FLAGS_OFFSET_RW 4
 #define ACPI_CPU_CMD_OFFSET_WR 5
 #define ACPI_CPU_CMD_DATA_OFFSET_RW 8
+#define ACPI_CPU_CMD_DATA2_OFFSET_R 0
 
 enum {
     CPHP_GET_NEXT_CPU_WITH_EVENT_CMD = 0,
@@ -79,6 +80,16 @@ static uint64_t cpu_hotplug_rd(void *opaque, hwaddr addr, unsigned size)
         }
         trace_cpuhp_acpi_read_cmd_data(cpu_st->selector, val);
         break;
+    case ACPI_CPU_CMD_DATA2_OFFSET_R:
+        switch (cpu_st->command) {
+        case CPHP_GET_NEXT_CPU_WITH_EVENT_CMD:
+           val = 0;
+           break;
+        default:
+           break;
+        }
+        trace_cpuhp_acpi_read_cmd_data2(cpu_st->selector, val);
+        break;
     default:
         break;
     }