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From:   "Rafael J. Wysocki" <rjw@rjwysocki.net>
To:     Linux PCI <linux-pci@vger.kernel.org>
Cc:     Linux PM <linux-pm@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Bjorn Helgaas <helgaas@kernel.org>,
        Mika Westerberg <mika.westerberg@linux.intel.com>
Subject: [PATCH v2 8/9] PCI/PM: Avoid redundant current_state update
Date:   Mon, 11 Apr 2022 16:31:45 +0200
Message-ID: <8938882.CDJkKcVGEf@kreacher>
In-Reply-To: <11975904.O9o76ZdvQC@kreacher>
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From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Notice that if pci_power_up() returns success early, without updating
the given device's PCI_PM_CTRL register, because it has verified that
the power state of the device is D0 already at that point, the
pci_update_current_state() invocation in pci_pm_default_resume_early()
is redundant.

Avoid that redundant call by making pci_power_up() return 1 when it
has updated the device's PCI_PM_CTRL register and checking its return
value in pci_pm_default_resume_early().

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---

New patch in v2.

---
 drivers/pci/pci-driver.c |    5 +++--
 drivers/pci/pci.c        |   10 ++++++++--
 2 files changed, 11 insertions(+), 4 deletions(-)

Index: linux-pm/drivers/pci/pci-driver.c
===================================================================
--- linux-pm.orig/drivers/pci/pci-driver.c
+++ linux-pm/drivers/pci/pci-driver.c
@@ -553,8 +553,9 @@ static void pci_pm_default_resume(struct
 
 static void pci_pm_default_resume_early(struct pci_dev *pci_dev)
 {
-	pci_power_up(pci_dev);
-	pci_update_current_state(pci_dev, PCI_D0);
+	if (pci_power_up(pci_dev))
+		pci_update_current_state(pci_dev, PCI_D0);
+
 	pci_restore_state(pci_dev);
 	pci_pme_restore(pci_dev);
 }
Index: linux-pm/drivers/pci/pci.c
===================================================================
--- linux-pm.orig/drivers/pci/pci.c
+++ linux-pm/drivers/pci/pci.c
@@ -1189,6 +1189,12 @@ static int pci_dev_wait(struct pci_dev *
 /**
  * pci_power_up - Put the given device into D0
  * @dev: PCI device to power up
+ *
+ * Use the platform firmware and the PCI_PM_CTRL register to put @dev into D0.
+ *
+ * Return 0 if invoking the platform firmware was sufficient to put @dev into D0
+ * (and so the PCI_PM_CTRL register was not updated), or 1 if it was necessary to
+ * update the PCI_PM_CTRL register, or -ENODEV if the device was not accessible.
  */
 int pci_power_up(struct pci_dev *dev)
 {
@@ -1235,7 +1241,7 @@ int pci_power_up(struct pci_dev *dev)
 		udelay(PCI_PM_D2_DELAY);
 
 	dev->current_state = PCI_D0;
-	return 0;
+	return 1;
 
 fail:
 	pci_err(dev, "Unable to change power state to D0, device inaccessible\n");
@@ -1273,7 +1279,7 @@ static int pci_set_full_power_state(stru
 	int ret;
 
 	ret = pci_power_up(dev);
-	if (ret)
+	if (ret < 0)
 		return ret;
 
 	if (!dev->pm_cap)