Commit 4c4cdc4c authored Aug 27, 2019 by Al Stone Committed by Rafael J. Wysocki Aug 28, 2019

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>

parent a55aa89a

drivers/acpi/cppc_acpi.c

+4 −2

Original line number	Diff line number	Diff line
		@@ -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;

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