On 8/26/19 5:02 PM, Rafael J. Wysocki wrote:
> On Tue, Aug 27, 2019 at 12:30 AM Al Stone <ahs3@xxxxxxxxxx> wrote:
>>
>> According to the ACPI 6.3 specification, the _PSD method is optional
>> when using CPPC. The underlying assumption is that each CPU can change
>> frequency independently from all other CPUs; _PSD is provided to tell
>> the OS that some processors can NOT do that.
>>
>> However, the acpi_get_psd() function returns ENODEV if there is no _PSD
>> method present, or an ACPI error status if an error occurs when evaluating
>> _PSD, if present. This makes _PSD mandatory when using CPPC, in violation
>> of the specification, and only on Linux.
>>
>> This has forced some firmware writers to provide a dummy _PSD, even though
>> it is irrelevant, but only because Linux requires it; other OSPMs follow
>> the spec. We really do not want to have OS specific ACPI tables, though.
>>
>> So, correct acpi_get_psd() so that it does not return an error if there
>> is no _PSD method present, but does return a failure when the method can
>> not be executed properly. This allows _PSD to be optional as it should
>> be.
>>
>> v2:
>> -- verified simple check for AE_NOT_FOUND was sufficient
>> -- simplified return status check per Rafael's suggestion
>>
>> Signed-off-by: Al Stone <ahs3@xxxxxxxxxx>
>> Cc: Rafael J. Wysocki <rjw@xxxxxxxxxxxxx>
>> Cc: Len Brown <lenb@xxxxxxxxxx>
>> ---
>> drivers/acpi/cppc_acpi.c | 10 ++++++----
>> 1 file changed, 6 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
>> index 15f103d7532b..7a946f1944ab 100644
>> --- a/drivers/acpi/cppc_acpi.c
>> +++ b/drivers/acpi/cppc_acpi.c
>> @@ -365,10 +365,12 @@ static int acpi_get_psd(struct cpc_desc *cpc_ptr, acpi_handle handle)
>> union acpi_object *psd = NULL;
>> struct acpi_psd_package *pdomain;
>>
>> - status = acpi_evaluate_object_typed(handle, "_PSD", NULL, &buffer,
>> - ACPI_TYPE_PACKAGE);
>> - if (ACPI_FAILURE(status))
>> - return -ENODEV;
>> + if (acpi_has_method(handle, "_PSD")) {
>
> This doesn't look necessary any more.
Probably true. I'll look back through acpi_evaluate_object_typed().
>> + status = acpi_evaluate_object_typed(handle, "_PSD", NULL,
>> + &buffer, ACPI_TYPE_PACKAGE);
>> + if (status == AE_NOT_FOUND) /* _PSD is optional */
>> + return 0;
>
> And what about the other possible errors?
Argh. My apologies. I was not paying attention. I'll correct
this and send proper code tomorrow. Really sorry for the noise :(...
>> + }
>>
>> psd = buffer.pointer;
>> if (!psd || psd->package.count != 1) {
>> --
>> 2.21.0
>>
--
ciao,
al
-----------------------------------
Al Stone
Software Engineer
Red Hat, Inc.
ahs3@xxxxxxxxxx
-----------------------------------
