[1/4] i386/acpi-build: more traditional _UID and _HID for PXB root buses

The ACPI specification permits the _HID and _UID objects to evaluate to
strings. (See "6.1.5 _HID (Hardware ID)" and "6.1.12 _UID (Unique ID)" in
the ACPI v6.0 spec.)

With regard to related standards, the UEFI specification can also express
a device address composed from string _HID and _UID identifiers, inside
the Expanded ACPI Device Path Node. (See "9.3.3 ACPI Device Path", Table
49, in the UEFI v2.5 spec.)

However, numeric (integer) contents for both _HID and _UID are more
traditional. They are recommended by the UEFI spec for size reasons:

  [...] the ACPI Device Path node is smaller and should be used if
  possible to reduce the size of device paths that may potentially be
  stored in nonvolatile storage [...]

External tools support them better (for example the --acpi_hid and
--acpi_uid options of "efibootmgr" only take numeric identifiers).
Finally, numeric _HID and _UID contents are existing practice in the QEMU
source.

This patch was tested with a Fedora 20 LiveCD and a preexistent Windows
Server 2012 R2 guest. Using "acpidump" and "iasl" in the Fedora guest, we
get, in the SSDT:

> Scope (\_SB)
> {
>   Device (PC04)
>   {
>     Name (_UID, 0x04)  // _UID: Unique ID
>     Name (_HID, EisaId ("PNP0A03") /* PCI Bus */)  // _HID: Hardware ID

Cc: Marcel Apfelbaum <marcel@redhat.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
---
 hw/i386/acpi-build.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

On 06/06/2015 02:46 AM, Laszlo Ersek wrote:
> The ACPI specification permits the _HID and _UID objects to evaluate to
> strings. (See "6.1.5 _HID (Hardware ID)" and "6.1.12 _UID (Unique ID)" in
> the ACPI v6.0 spec.)
>
> With regard to related standards, the UEFI specification can also express
> a device address composed from string _HID and _UID identifiers, inside
> the Expanded ACPI Device Path Node. (See "9.3.3 ACPI Device Path", Table
> 49, in the UEFI v2.5 spec.)
>
> However, numeric (integer) contents for both _HID and _UID are more
> traditional. They are recommended by the UEFI spec for size reasons:
>
>    [...] the ACPI Device Path node is smaller and should be used if
>    possible to reduce the size of device paths that may potentially be
>    stored in nonvolatile storage [...]
>
> External tools support them better (for example the --acpi_hid and
> --acpi_uid options of "efibootmgr" only take numeric identifiers).
> Finally, numeric _HID and _UID contents are existing practice in the QEMU
> source.
>
> This patch was tested with a Fedora 20 LiveCD and a preexistent Windows
> Server 2012 R2 guest. Using "acpidump" and "iasl" in the Fedora guest, we
> get, in the SSDT:
>
>> Scope (\_SB)
>> {
>>    Device (PC04)
>>    {
>>      Name (_UID, 0x04)  // _UID: Unique ID
>>      Name (_HID, EisaId ("PNP0A03") /* PCI Bus */)  // _HID: Hardware ID
>
> Cc: Marcel Apfelbaum <marcel@redhat.com>
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Laszlo Ersek <lersek@redhat.com>
> ---
>   hw/i386/acpi-build.c | 5 ++---
>   1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
> index 5593e41..52c2591 100644
> --- a/hw/i386/acpi-build.c
> +++ b/hw/i386/acpi-build.c
> @@ -945,9 +945,8 @@ build_ssdt(GArray *table_data, GArray *linker,
>
>               scope = aml_scope("\\_SB");
>               dev = aml_device("PC%.02X", bus_num);
> -            aml_append(dev,
> -                       aml_name_decl("_UID", aml_string("PC%.02X", bus_num)));
> -            aml_append(dev, aml_name_decl("_HID", aml_string("PNP0A03")));
> +            aml_append(dev, aml_name_decl("_UID", aml_int(bus_num)));
> +            aml_append(dev, aml_name_decl("_HID", aml_eisaid("PNP0A03")));
>               aml_append(dev, aml_name_decl("_BBN", aml_int(bus_num)));
>
>               if (numa_node != NUMA_NODE_UNASSIGNED) {
>

Reviewed-by: Marcel Apfelbaum <marcel@redhat.com>


Thanks,
Marcel