PCI: Track Flit Mode Status & print it with link status

PCIe r6.0 added Flit mode, which mainly alters HW behavior, but there are
some OS visible changes. The OS visible changes include differences in the
layout of some capabilities and interpretation of the TLP headers (in
diagnostics situations).

To be able to determine which mode the PCIe Link is using, store the Flit
Mode Status (PCIe r6.1 sec 7.5.3.20) information in addition to the Link
speed into struct pci_bus in pcie_update_link_speed().

Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Ilpo Järvinen <[email protected]>
[bhelgaas: use unsigned int:1 instead of bool, update flit_mode setting]
Signed-off-by: Bjorn Helgaas <[email protected]>

Author: ij-intel

drivers/pci/hotplug/pciehp_hpc.c

@@ -292,7 +292,7 @@ int pciehp_check_link_status(struct controller *ctrl)
 {
 	struct pci_dev *pdev = ctrl_dev(ctrl);
 	bool found;
-	u16 lnk_status;
+	u16 lnk_status, linksta2;
 
 	if (!pcie_wait_for_link(pdev, true)) {
 		ctrl_info(ctrl, "Slot(%s): No link\n", slot_name(ctrl));
@@ -319,7 +319,8 @@ int pciehp_check_link_status(struct controller *ctrl)
 		return -1;
 	}
 
-	__pcie_update_link_speed(ctrl->pcie->port->subordinate, lnk_status);
+	pcie_capability_read_word(pdev, PCI_EXP_LNKSTA2, &linksta2);
+	__pcie_update_link_speed(ctrl->pcie->port->subordinate, lnk_status, linksta2);
 
 	if (!found) {
 		ctrl_info(ctrl, "Slot(%s): No device found\n",

drivers/pci/pci.c

@@ -6190,21 +6190,25 @@ void __pcie_print_link_status(struct pci_dev *dev, bool verbose)
 	enum pci_bus_speed speed, speed_cap;
 	struct pci_dev *limiting_dev = NULL;
 	u32 bw_avail, bw_cap;
+	char *flit_mode = "";
 
 	bw_cap = pcie_bandwidth_capable(dev, &speed_cap, &width_cap);
 	bw_avail = pcie_bandwidth_available(dev, &limiting_dev, &speed, &width);
 
+	if (dev->bus && dev->bus->flit_mode)
+		flit_mode = ", in Flit mode";
+
 	if (bw_avail >= bw_cap && verbose)
-		pci_info(dev, "%u.%03u Gb/s available PCIe bandwidth (%s x%d link)\n",
+		pci_info(dev, "%u.%03u Gb/s available PCIe bandwidth (%s x%d link)%s\n",
 			 bw_cap / 1000, bw_cap % 1000,
-			 pci_speed_string(speed_cap), width_cap);
+			 pci_speed_string(speed_cap), width_cap, flit_mode);
 	else if (bw_avail < bw_cap)
-		pci_info(dev, "%u.%03u Gb/s available PCIe bandwidth, limited by %s x%d link at %s (capable of %u.%03u Gb/s with %s x%d link)\n",
+		pci_info(dev, "%u.%03u Gb/s available PCIe bandwidth, limited by %s x%d link at %s (capable of %u.%03u Gb/s with %s x%d link)%s\n",
 			 bw_avail / 1000, bw_avail % 1000,
 			 pci_speed_string(speed), width,
 			 limiting_dev ? pci_name(limiting_dev) : "<unknown>",
 			 bw_cap / 1000, bw_cap % 1000,
-			 pci_speed_string(speed_cap), width_cap);
+			 pci_speed_string(speed_cap), width_cap, flit_mode);
 }
 
 /**

drivers/pci/pci.h

@@ -406,9 +406,10 @@ const char *pci_speed_string(enum pci_bus_speed speed);
 void __pcie_print_link_status(struct pci_dev *dev, bool verbose);
 void pcie_report_downtraining(struct pci_dev *dev);
 
-static inline void __pcie_update_link_speed(struct pci_bus *bus, u16 linksta)
+static inline void __pcie_update_link_speed(struct pci_bus *bus, u16 linksta, u16 linksta2)
 {
 	bus->cur_bus_speed = pcie_link_speed[linksta & PCI_EXP_LNKSTA_CLS];
+	bus->flit_mode = (linksta2 & PCI_EXP_LNKSTA2_FLIT) ? 1 : 0;
 }
 void pcie_update_link_speed(struct pci_bus *bus);
 

drivers/pci/probe.c

@@ -788,10 +788,11 @@ EXPORT_SYMBOL_GPL(pci_speed_string);
 void pcie_update_link_speed(struct pci_bus *bus)
 {
 	struct pci_dev *bridge = bus->self;
-	u16 linksta;
+	u16 linksta, linksta2;
 
 	pcie_capability_read_word(bridge, PCI_EXP_LNKSTA, &linksta);
-	__pcie_update_link_speed(bus, linksta);
+	pcie_capability_read_word(bridge, PCI_EXP_LNKSTA2, &linksta2);
+	__pcie_update_link_speed(bus, linksta, linksta2);
 }
 EXPORT_SYMBOL_GPL(pcie_update_link_speed);
 

include/linux/pci.h

@@ -681,6 +681,7 @@ struct pci_bus {
 	struct bin_attribute	*legacy_mem;	/* Legacy mem */
 	unsigned int		is_added:1;
 	unsigned int		unsafe_warn:1;	/* warned about RW1C config write */
+	unsigned int		flit_mode:1;	/* Link in Flit mode */
 };
 
 #define to_pci_bus(n)	container_of(n, struct pci_bus, dev)