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

[Laszlo Ersek <lersek@redhat.com>]

On 12/09/19 14:09, Igor Mammedov wrote:
> 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"]"
> 

Neat. :)

Reviewed-by: Laszlo Ersek <lersek@redhat.com>