linux-kernel - [PATCH 9/10] PCI PM: Make pci_set_power_state() handle devices with no PM support

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Date:	Wed, 11 Mar 2009 10:55:50 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	pm list <linux-pm@...ts.linux-foundation.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Len Brown <lenb@...nel.org>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Frans Pop <elendil@...net.nl>,
	Arve Hjønnevåg <arve@...roid.com>
Subject: [PATCH 9/10] PCI PM: Make pci_set_power_state() handle devices with no PM support

From: Rafael J. Wysocki <rjw@...k.pl>

There is a problem with PCI devices without any PM support (either native or
through the platform) that pci_set_power_state() always returns error code for
them, even if they are being put into D0.  However, such devices are always in
D0, so pci_set_power_state() should return success when attempting to put such a
device into D0.  It also should update the current_state field for these
devices as appropriate.  This modification is necessary so that the standard
configuration registers of these devices are successfully restored by
pci_restore_standard_config() during the "early" phase of resume.

In addition, pci_set_power_state() should check the value of current_state
before calling the platform to change the power state of the device to avoid
doing that unnecessarily.

Signed-off-by: Rafael J. Wysocki <rjw@...k.pl>
---
 drivers/pci/pci.c |   18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

Index: linux-2.6/drivers/pci/pci.c
===================================================================
--- linux-2.6.orig/drivers/pci/pci.c
+++ linux-2.6/drivers/pci/pci.c
@@ -439,6 +439,10 @@ static int pci_raw_set_power_state(struc
 	u16 pmcsr;
 	bool need_restore = false;
 
+	/* Check if we're already there */
+	if (dev->current_state == state)
+		return 0;
+
 	if (!dev->pm_cap)
 		return -EIO;
 
@@ -449,10 +453,7 @@ static int pci_raw_set_power_state(struc
 	 * Can enter D0 from any state, but if we can only go deeper 
 	 * to sleep if we're already in a low power state
 	 */
-	if (dev->current_state == state) {
-		/* we're already there */
-		return 0;
-	} else if (state != PCI_D0 && dev->current_state <= PCI_D3cold
+	if (state != PCI_D0 && dev->current_state <= PCI_D3cold
 	    && dev->current_state > state) {
 		dev_err(&dev->dev, "invalid power transition "
 			"(from state %d to %d)\n", dev->current_state, state);
@@ -570,12 +571,17 @@ int pci_set_power_state(struct pci_dev *
 		 */
 		return 0;
 
-	if (state == PCI_D0 && platform_pci_power_manageable(dev)) {
+	/* Check if we're already there */
+	if (dev->current_state == state)
+		return 0;
+
+	if (state == PCI_D0) {
 		/*
 		 * Allow the platform to change the state, for example via ACPI
 		 * _PR0, _PS0 and some such, but do not trust it.
 		 */
-		int ret = platform_pci_set_power_state(dev, PCI_D0);
+		int ret = platform_pci_power_manageable(dev) ?
+			platform_pci_set_power_state(dev, PCI_D0) : 0;
 		if (!ret)
 			pci_update_current_state(dev, PCI_D0);
 	}
--
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