diff options
author | Al Stone <ahs3@redhat.com> | 2019-08-27 18:21:20 -0600 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2019-10-05 12:27:49 +0200 |
commit | 318e486d4ed967187b91957d1683b8e75e2b1ea6 (patch) | |
tree | 8428551f72fc59c889b97ef3a2ebefe247a4b87d | |
parent | 7ff7d1e7a749843920201489aaed20154eff5a15 (diff) |
ACPI / CPPC: do not require the _PSD method
[ Upstream commit 4c4cdc4c63853fee48c02e25c8605fb65a6c9924 ]
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.
Signed-off-by: Al Stone <ahs3@redhat.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
-rw-r--r-- | drivers/acpi/cppc_acpi.c | 6 |
1 files changed, 4 insertions, 2 deletions
diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c index 0afd1981e350..43c27c04c40a 100644 --- a/drivers/acpi/cppc_acpi.c +++ b/drivers/acpi/cppc_acpi.c @@ -137,8 +137,10 @@ 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); + status = acpi_evaluate_object_typed(handle, "_PSD", NULL, + &buffer, ACPI_TYPE_PACKAGE); + if (status == AE_NOT_FOUND) /* _PSD is optional */ + return 0; if (ACPI_FAILURE(status)) return -ENODEV; |