agp/nvidia: Convert to generic power management

Convert agpgart-nvidia from legacy PCI power management to the generic
power management framework.

Previously agpgart-nvidia used legacy PCI power management, and
agp_nvidia_suspend() and agp_nvidia_resume() were responsible for both
device-specific things and generic PCI things:

  agp_nvidia_suspend
    pci_save_state                         <-- generic PCI
    pci_set_power_state(PCI_D3hot)         <-- generic PCI

  agp_nvidia_resume
    pci_set_power_state(PCI_D0)            <-- generic PCI
    pci_restore_state                      <-- generic PCI
    nvidia_configure                       <-- device-specific

Convert to generic power management where the PCI bus PM methods do the
generic PCI things, and the driver needs only the device-specific part,
i.e.,

  suspend_devices_and_enter
    dpm_suspend_start(PMSG_SUSPEND)
      pci_pm_suspend                       # PCI bus .suspend() method
        agp_nvidia_suspend                 <-- not needed at all; removed
    suspend_enter
      dpm_suspend_noirq(PMSG_SUSPEND)
        pci_pm_suspend_noirq               # PCI bus .suspend_noirq() method
          pci_save_state                   <-- generic PCI
          pci_prepare_to_sleep             <-- generic PCI
            pci_set_power_state
    ...
    dpm_resume_end(PMSG_RESUME)
      pci_pm_resume                        # PCI bus .resume() method
        pci_restore_standard_config
          pci_set_power_state(PCI_D0)      <-- generic PCI
          pci_restore_state                <-- generic PCI
        agp_nvidia_resume                  # driver->pm->resume
          nvidia_configure                 <-- device-specific

Based on 0aeddbd0 ("via-agp: convert to generic power management") by
Vaibhav Gupta <vaibhavgupta40@gmail.com>.

Link: https://lore.kernel.org/r/20221025203852.681822-6-helgaas@kernel.orgSigned-off-by: NBjorn Helgaas <bhelgaas@google.com>
Acked-by: NDave Airlie <airlied@redhat.com>

drivers/char/agp/nvidia-agp.c

@@ -404,28 +404,13 @@ static void agp_nvidia_remove(struct pci_dev *pdev)
 	agp_put_bridge(bridge);
 }
 
-#ifdef CONFIG_PM
-static int agp_nvidia_suspend(struct pci_dev *pdev, pm_message_t state)
+static int agp_nvidia_resume(struct device *dev)
 {
-	pci_save_state(pdev);
-	pci_set_power_state(pdev, PCI_D3hot);
-
-	return 0;
-}
-
-static int agp_nvidia_resume(struct pci_dev *pdev)
-{
-	/* set power state 0 and restore PCI space */
-	pci_set_power_state(pdev, PCI_D0);
-	pci_restore_state(pdev);
-
 	/* reconfigure AGP hardware again */
 	nvidia_configure();
 
 	return 0;
 }
-#endif
-
 
 static const struct pci_device_id agp_nvidia_pci_table[] = {
 	{
@@ -449,15 +434,14 @@ static const struct pci_device_id agp_nvidia_pci_table[] = {
 
 MODULE_DEVICE_TABLE(pci, agp_nvidia_pci_table);
 
+static DEFINE_SIMPLE_DEV_PM_OPS(agp_nvidia_pm_ops, NULL, agp_nvidia_resume);
+
 static struct pci_driver agp_nvidia_pci_driver = {
 	.name		= "agpgart-nvidia",
 	.id_table	= agp_nvidia_pci_table,
 	.probe		= agp_nvidia_probe,
 	.remove		= agp_nvidia_remove,
-#ifdef CONFIG_PM
-	.suspend	= agp_nvidia_suspend,
-	.resume		= agp_nvidia_resume,
-#endif
+	.driver.pm	= &agp_nvidia_pm_ops,
 };
 
 static int __init agp_nvidia_init(void)