[PATCH for-5.0 v2 7/9] acpi: cpuhp: introduce 'Command data 2' field

[Igor Mammedov <imammedo@redhat.com>]

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>
---
 docs/specs/acpi_cpu_hotplug.txt |  5 ++++-
 hw/acpi/cpu.c                   | 11 +++++++++++
 hw/acpi/trace-events            |  1 +
 3 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/docs/specs/acpi_cpu_hotplug.txt b/docs/specs/acpi_cpu_hotplug.txt
index 8fb9ad2..9879f9e 100644
--- a/docs/specs/acpi_cpu_hotplug.txt
+++ b/docs/specs/acpi_cpu_hotplug.txt
@@ -44,7 +44,10 @@ keeps the current value.
 
 read access:
     offset:
-    [0x0-0x3] reserved
+    [0x0-0x3] Command data 2: (DWORD access)
+              if value last stored in 'Command field':
+                0: reads as 0x0
+                other values: reserved
     [0x4] CPU device status fields: (1 byte access)
         bits:
            0: Device is enabled and may be used by guest
diff --git a/hw/acpi/cpu.c b/hw/acpi/cpu.c
index 87f30a3..d475c06 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;
     }
diff --git a/hw/acpi/trace-events b/hw/acpi/trace-events
index 96b8273..afbc77d 100644
--- a/hw/acpi/trace-events
+++ b/hw/acpi/trace-events
@@ -23,6 +23,7 @@ cpuhp_acpi_read_flags(uint32_t idx, uint8_t flags) "idx[0x%"PRIx32"] flags: 0x%"
 cpuhp_acpi_write_idx(uint32_t idx) "set active cpu idx: 0x%"PRIx32
 cpuhp_acpi_write_cmd(uint32_t idx, uint8_t cmd) "idx[0x%"PRIx32"] cmd: 0x%"PRIx8
 cpuhp_acpi_read_cmd_data(uint32_t idx, uint32_t data) "idx[0x%"PRIx32"] data: 0x%"PRIx32
+cpuhp_acpi_read_cmd_data2(uint32_t idx, uint32_t data) "idx[0x%"PRIx32"] data: 0x%"PRIx32
 cpuhp_acpi_cpu_has_events(uint32_t idx, bool ins, bool rm) "idx[0x%"PRIx32"] inserting: %d, removing: %d"
 cpuhp_acpi_clear_inserting_evt(uint32_t idx) "idx[0x%"PRIx32"]"
 cpuhp_acpi_clear_remove_evt(uint32_t idx) "idx[0x%"PRIx32"]"
-- 
2.7.4