[PATCH v9 1/5] PCI: Add pcie_get_link_speed() helper for safe array access

[Hans Zhang <18255117159@163.com>]

The pcie_link_speed[] array is indexed by PCIe generation numbers
(1 = 2.5 GT/s, 2 = 5 GT/s, ...).  Several drivers use it directly,
which can lead to out-of-bounds accesses if an invalid generation
number is used.

Introduce a helper function pcie_get_link_speed() that returns the
corresponding enum pci_bus_speed value for a given generation number,
or PCI_SPEED_UNKNOWN if the generation is out of range.  This will
allow us to safely handle invalid values after the range check is
removed from of_pci_get_max_link_speed().

Signed-off-by: Hans Zhang <18255117159@163.com>
---
 drivers/pci/pci.h   |  2 ++
 drivers/pci/probe.c | 16 ++++++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index 13d998fbacce..409aca7d737a 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -108,6 +108,8 @@ struct pcie_tlp_log;
 				 PCI_EXP_DEVCTL_FERE | PCI_EXP_DEVCTL_URRE)
 
 extern const unsigned char pcie_link_speed[];
+unsigned char pcie_get_link_speed(unsigned int speed);
+
 extern bool pci_early_dump;
 
 extern struct mutex pci_rescan_remove_lock;
diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index bccc7a4bdd79..d6592898330c 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -783,6 +783,22 @@ const unsigned char pcie_link_speed[] = {
 };
 EXPORT_SYMBOL_GPL(pcie_link_speed);
 
+/**
+ * pcie_link_speed_value - Get speed value from PCIe generation number
+ * @speed: PCIe speed (1-based: 1 = 2.5GT, 2 = 5GT, ...)
+ *
+ * Returns the speed value (e.g., PCIE_SPEED_2_5GT) if @speed is valid,
+ * otherwise returns PCI_SPEED_UNKNOWN.
+ */
+unsigned char pcie_get_link_speed(unsigned int speed)
+{
+	if (speed >= ARRAY_SIZE(pcie_link_speed))
+		return PCI_SPEED_UNKNOWN;
+
+	return pcie_link_speed[speed];
+}
+EXPORT_SYMBOL_GPL(pcie_get_link_speed);
+
 const char *pci_speed_string(enum pci_bus_speed speed)
 {
 	/* Indexed by the pci_bus_speed enum */
-- 
2.34.1