linux-kernel - [PATCH][RFT] PCI: Use pci_update_current_state() in pci_enable_device

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Date:   Thu, 08 Jul 2021 15:25:06 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Maximilian Luz <luzmaximilian@...il.com>
Cc:     Linux PCI <linux-pci@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>
Subject: [PATCH][RFT] PCI: Use pci_update_current_state() in pci_enable_device_flags()

From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

Updating the current_state field of struct pci_dev the way it is done
in pci_enable_device_flags() before calling do_pci_enable_device() may
not work.  For example, if the given PCI device depends on an ACPI
power resource whose _STA method initially returns 0 ("off"), but the
config space of the PCI device is accessible and the power state
retrieved from the PCI_PM_CTRL register is D0, the current_state
field in the struct pci_dev representing that device will get out of
sync with the power.state of its ACPI companion object and that will
lead to power management issues going forward.

To avoid such issues, make pci_enable_device_flags() call
pci_update_current_state() which takes ACPI device power management
into account, if present, to retrieve the current power state of the
device.

Link: https://lore.kernel.org/lkml/20210314000439.3138941-1-luzmaximilian@gmail.com/
Reported-by: Maximilian Luz <luzmaximilian@...il.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
---

Hi Maximilian,

Because commit 4514d991d992 ("PCI: PM: Do not read power state in
pci_enable_device_flags()"), the issue addressed by it is back, so
we need an alternative way to address it.

Can you please check if this patch makes that issue go away?

Thanks!

---
 drivers/pci/pci.c |    6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

Index: linux-pm/drivers/pci/pci.c
===================================================================
--- linux-pm.orig/drivers/pci/pci.c
+++ linux-pm/drivers/pci/pci.c
@@ -1906,11 +1906,7 @@ static int pci_enable_device_flags(struc
 	 * so that things like MSI message writing will behave as expected
 	 * (e.g. if the device really is in D0 at enable time).
 	 */
-	if (dev->pm_cap) {
-		u16 pmcsr;
-		pci_read_config_word(dev, dev->pm_cap + PCI_PM_CTRL, &pmcsr);
-		dev->current_state = (pmcsr & PCI_PM_CTRL_STATE_MASK);
-	}
+	pci_update_current_state(dev, dev->current_state);

 	if (atomic_inc_return(&dev->enable_cnt) > 1)
 		return 0;		/* already enabled */