PCI/sysfs: Protect driver's D3cold preference from user space

struct pci_dev contains two flags which govern whether the device may
suspend to D3cold:

* no_d3cold provides an opt-out for drivers (e.g. if a device is known
  to not wake from D3cold)

* d3cold_allowed provides an opt-out for user space (default is true,
  user space may set to false)

Since commit 9d26d3a ("PCI: Put PCIe ports into D3 during suspend"),
the user space setting overwrites the driver setting.  Essentially user
space is trusted to know better than the driver whether D3cold is
working.

That feels unsafe and wrong.  Assume that the change was introduced
inadvertently and do not overwrite no_d3cold when d3cold_allowed is
modified.  Instead, consider d3cold_allowed in addition to no_d3cold
when choosing a suspend state for the device.

That way, user space may opt out of D3cold if the driver hasn't, but it
may no longer force an opt in if the driver has opted out.

Fixes: 9d26d3a ("PCI: Put PCIe ports into D3 during suspend")
Link: https://lore.kernel.org/r/b8a7f4af2b73f6b506ad8ddee59d747cbf834606.1695025365.git.lukas@wunner.de
Signed-off-by: Lukas Wunner <[email protected]>
Signed-off-by: Bjorn Helgaas <[email protected]>
Reviewed-by: Mika Westerberg <[email protected]>
Reviewed-by: Mario Limonciello <[email protected]>
Cc: [email protected]	# v4.8+

Author: l1k

drivers/pci/pci-acpi.c

@@ -911,7 +911,7 @@ pci_power_t acpi_pci_choose_state(struct pci_dev *pdev)
 {
 	int acpi_state, d_max;
 
-	if (pdev->no_d3cold)
+	if (pdev->no_d3cold || !pdev->d3cold_allowed)
 		d_max = ACPI_STATE_D3_HOT;
 	else
 		d_max = ACPI_STATE_D3_COLD;

drivers/pci/pci-sysfs.c

@@ -530,10 +530,7 @@ static ssize_t d3cold_allowed_store(struct device *dev,
 		return -EINVAL;
 
 	pdev->d3cold_allowed = !!val;
-	if (pdev->d3cold_allowed)
-		pci_d3cold_enable(pdev);
-	else
-		pci_d3cold_disable(pdev);
+	pci_bridge_d3_update(pdev);
 
 	pm_runtime_resume(dev);