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>

1 files changed, 53 insertions, 0 deletions

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 44d1c7c3876b..d0182bed7acc 100644
--- a/drivers/pci/pci.c
+++ b/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;
 
 /**