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")) {
+ status = acpi_evaluate_object_typed(handle, "_PSD", NULL,
+ &buffer, ACPI_TYPE_PACKAGE);
+ if (status == AE_NOT_FOUND) /* _PSD is optional */
+ return 0;
+ }
psd = buffer.pointer;
if (!psd || psd->package.count != 1) {
--
2.21.0
