PCI: Support Immediate Readiness on devices without PM capabilities

Query support for Immediate Readiness irrespective of whether or not the
device supports PM capabilities, as nothing in the PCIe spec suggests that
Immediate Readiness is in any way dependent on PM functionality.

Fixes: d6112f8 ("PCI: Add support for Immediate Readiness")
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: David Matlack <dmatlack@google.com>
Cc: Vipin Sharma <vipinsh@google.com>
Cc: Aaron Lewis <aaronlewis@google.com>
Link: https://patch.msgid.link/20250722155926.352248-1-seanjc@google.com

Author: sean-jc

drivers/pci/pci.c

@@ -3205,7 +3205,6 @@ void pci_pm_power_up_and_verify_state(struct pci_dev *pci_dev)
 void pci_pm_init(struct pci_dev *dev)
 {
 	int pm;
-	u16 status;
 	u16 pmc;
 
 	device_enable_async_suspend(&dev->dev);
@@ -3266,9 +3265,6 @@ void pci_pm_init(struct pci_dev *dev)
 		pci_pme_active(dev, false);
 	}
 
-	pci_read_config_word(dev, PCI_STATUS, &status);
-	if (status & PCI_STATUS_IMM_READY)
-		dev->imm_ready = 1;
 	pci_pm_power_up_and_verify_state(dev);
 	pm_runtime_forbid(&dev->dev);
 	pm_runtime_set_active(&dev->dev);

drivers/pci/probe.c

@@ -2595,6 +2595,15 @@ void pcie_report_downtraining(struct pci_dev *dev)
 	__pcie_print_link_status(dev, false);
 }
 
+static void pci_imm_ready_init(struct pci_dev *dev)
+{
+	u16 status;
+
+	pci_read_config_word(dev, PCI_STATUS, &status);
+	if (status & PCI_STATUS_IMM_READY)
+		dev->imm_ready = 1;
+}
+
 static void pci_init_capabilities(struct pci_dev *dev)
 {
 	pci_ea_init(dev);		/* Enhanced Allocation */
@@ -2604,6 +2613,7 @@ static void pci_init_capabilities(struct pci_dev *dev)
 	/* Buffers for saving PCIe and PCI-X capabilities */
 	pci_allocate_cap_save_buffers(dev);
 
+	pci_imm_ready_init(dev);	/* Immediate Readiness */
 	pci_pm_init(dev);		/* Power Management */
 	pci_vpd_init(dev);		/* Vital Product Data */
 	pci_configure_ari(dev);		/* Alternative Routing-ID Forwarding */