PCI: add ID-based ordering enable/disable support

Add support to allow drivers to enable/disable ID-based ordering.  Where
supported, ID-based ordering can significantly improve the latency of
individual requests by preventing them from queueing up behind unrelated
traffic.
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

drivers/pci/pci.c

@@ -1834,6 +1834,59 @@ void pci_enable_ari(struct pci_dev *dev)
 	bridge->ari_enabled = 1;
 }
 
+/**
+ * pci_enable_ido - enable ID-based ordering on a device
+ * @dev: the PCI device
+ * @type: which types of IDO to enable
+ *
+ * Enable ID-based ordering on @dev.  @type can contain the bits
+ * %PCI_EXP_IDO_REQUEST and/or %PCI_EXP_IDO_COMPLETION to indicate
+ * which types of transactions are allowed to be re-ordered.
+ */
+void pci_enable_ido(struct pci_dev *dev, unsigned long type)
+{
+	int pos;
+	u16 ctrl;
+
+	pos = pci_pcie_cap(dev);
+	if (!pos)
+		return;
+
+	pci_read_config_word(dev, pos + PCI_EXP_DEVCTL2, &ctrl);
+	if (type & PCI_EXP_IDO_REQUEST)
+		ctrl |= PCI_EXP_IDO_REQ_EN;
+	if (type & PCI_EXP_IDO_COMPLETION)
+		ctrl |= PCI_EXP_IDO_CMP_EN;
+	pci_write_config_word(dev, pos + PCI_EXP_DEVCTL2, ctrl);
+}
+EXPORT_SYMBOL(pci_enable_ido);
+
+/**
+ * pci_disable_ido - disable ID-based ordering on a device
+ * @dev: the PCI device
+ * @type: which types of IDO to disable
+ */
+void pci_disable_ido(struct pci_dev *dev, unsigned long type)
+{
+	int pos;
+	u16 ctrl;
+
+	if (!pci_is_pcie(dev))
+		return;
+
+	pos = pci_pcie_cap(dev);
+	if (!pos)
+		return;
+
+	pci_read_config_word(dev, pos + PCI_EXP_DEVCTL2, &ctrl);
+	if (type & PCI_EXP_IDO_REQUEST)
+		ctrl &= ~PCI_EXP_IDO_REQ_EN;
+	if (type & PCI_EXP_IDO_COMPLETION)
+		ctrl &= ~PCI_EXP_IDO_CMP_EN;
+	pci_write_config_word(dev, pos + PCI_EXP_DEVCTL2, ctrl);
+}
+EXPORT_SYMBOL(pci_disable_ido);
+
 static int pci_acs_enable;
 
 /**

include/linux/pci.h

@@ -828,6 +828,11 @@ static inline int pci_enable_wake(struct pci_dev *dev, pci_power_t state,
 	return __pci_enable_wake(dev, state, false, enable);
 }
 
+#define PCI_EXP_IDO_REQUEST	(1<<0)
+#define PCI_EXP_IDO_COMPLETION	(1<<1)
+void pci_enable_ido(struct pci_dev *dev, unsigned long type);
+void pci_disable_ido(struct pci_dev *dev, unsigned long type);
+
 /* For use by arch with custom probe code */
 void set_pcie_port_type(struct pci_dev *pdev);
 void set_pcie_hotplug_bridge(struct pci_dev *pdev);
@@ -1207,6 +1212,14 @@ static inline int pci_enable_wake(struct pci_dev *dev, pci_power_t state,
 	return 0;
 }
 
+static inline void pci_enable_ido(struct pci_dev *dev, unsigned long type)
+{
+}
+
+static inline void pci_disable_ido(struct pci_dev *dev, unsigned long type)
+{
+}
+
 static inline int pci_request_regions(struct pci_dev *dev, const char *res_name)
 {
 	return -EIO;

include/linux/pci_regs.h

@@ -510,6 +510,8 @@
 #define  PCI_EXP_DEVCAP2_ARI	0x20	/* Alternative Routing-ID */
 #define PCI_EXP_DEVCTL2		40	/* Device Control 2 */
 #define  PCI_EXP_DEVCTL2_ARI	0x20	/* Alternative Routing-ID */
+#define  PCI_EXP_IDO_REQ_EN	0x100	/* ID-based ordering request enable */
+#define  PCI_EXP_IDO_CMP_EN	0x200	/* ID-based ordering completion enable */
 #define PCI_EXP_LNKCTL2		48	/* Link Control 2 */
 #define PCI_EXP_SLTCTL2		56	/* Slot Control 2 */