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From: Sasha Levin <sashal@kernel.org>
To: linux-kernel@vger.kernel.org, stable@vger.kernel.org
Cc: Al Stone <ahs3@redhat.com>,
	"Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
	Sasha Levin <sashal@kernel.org>,
	linux-acpi@vger.kernel.org
Subject: [PATCH AUTOSEL 4.14 61/89] ACPI / CPPC: do not require the _PSD method
Date: Sun, 22 Sep 2019 14:56:49 -0400
Message-ID: <20190922185717.3412-61-sashal@kernel.org> (raw)
In-Reply-To: <20190922185717.3412-1-sashal@kernel.org>

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 e5b47f032d9af..7bf1948b1223b 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;
 
-- 
2.20.1


  parent reply index

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20190922185717.3412-1-sashal@kernel.org>
2019-09-22 18:56 ` [PATCH AUTOSEL 4.14 28/89] ACPI / processor: don't print errors for processorIDs == 0xff Sasha Levin
2019-09-22 18:56 ` Sasha Levin [this message]
2019-09-22 18:56 ` [PATCH AUTOSEL 4.14 68/89] ACPI: custom_method: fix memory leaks Sasha Levin
2019-09-22 18:56 ` [PATCH AUTOSEL 4.14 69/89] ACPI / PCI: fix acpi_pci_irq_enable() memory leak Sasha Levin

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