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Subject[PATCH AUTOSEL 4.4 30/44] ACPI / CPPC: do not require the _PSD method
Date
From: Al Stone <ahs3@redhat.com>

[ 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>
---
drivers/acpi/cppc_acpi.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
index 0afd1981e350b..43c27c04c40ae 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;

--
2.20.1
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