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authorAl Stone <ahs3@redhat.com>2019-08-27 18:21:20 -0600
committerRafael J. Wysocki <rafael.j.wysocki@intel.com>2019-08-28 11:20:33 +0200
commit4c4cdc4c63853fee48c02e25c8605fb65a6c9924 (patch)
tree154a40bdaa74b4122e50ec031a45a38a973aa7a5 /drivers/acpi/cppc_acpi.c
parenta55aa89aab90fae7c815b0551b07be37db359d76 (diff)
downloadlinux-4c4cdc4c63853fee48c02e25c8605fb65a6c9924.tar.bz2
ACPI / CPPC: do not require the _PSD method
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>
Diffstat (limited to 'drivers/acpi/cppc_acpi.c')
-rw-r--r--drivers/acpi/cppc_acpi.c6
1 files changed, 4 insertions, 2 deletions
diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
index 15f103d7532b..3b2525908dd8 100644
--- a/drivers/acpi/cppc_acpi.c
+++ b/drivers/acpi/cppc_acpi.c
@@ -365,8 +365,10 @@ 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;