Re: [Qemu-devel] [PATCH v2] i386/acpi: add _HID to processor objects

[Matthias Lange]

On 10/23/2015 03:08 PM, Igor Mammedov wrote:
> On Thu, 22 Oct 2015 22:03:24 +0200
> Matthias Lange <address@hidden> wrote:
> 
>> This patch appends "ACPI0007" as the HID to each processor object.
>>
>> Until commit 20843d processor objects used to have a _HID. According
>> to the ACPI spec this is not required but removing it breaks systems
> Pls answer Michael's question about motivation of this patch.
>  i.e. what guests it exactly breaks?

It broke the L4Re OS (specifically the mechanism to match ACPI drivers
to ACPI devices).

However, you can ignore this patch. I decided to change L4Re instead.

Best,
Matthias.

>> which relied on the HID. As it does no harm it is safe to add _HID
>> to processor objects and restore the old behaviour.
>>
>> Signed-off-by: Matthias Lange <address@hidden>
>> ---
>>  hw/i386/acpi-build.c | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
>> index 95e0c65..314cd0b 100644
>> --- a/hw/i386/acpi-build.c
>> +++ b/hw/i386/acpi-build.c
>> @@ -1153,6 +1153,9 @@ build_ssdt(GArray *table_data, GArray *linker,
>>          for (i = 0; i < acpi_cpus; i++) {
>>              dev = aml_processor(i, 0, 0, "CP%.02X", i);
>>  
>> +            /* for processor objects a _HID is not strictly required, 
>> however it
>> +             * does no harm and preserves compatibility with other BIOSes */
>> +            aml_append(dev, aml_name_decl("_HID", aml_string("ACPI0007")));
> Spec doesn't tell anything about using ACPI0007 with Processor statement,
> it's only mentioned in context of Device statement.
> 
>>              method = aml_method("_MAT", 0);
>>              aml_append(method, aml_return(aml_call1("CPMA", aml_int(i))));
>>              aml_append(dev, method);