PCI: add OBFF enable/disable support

OBFF (optimized buffer flush/fill), where supported, can help improve
energy efficiency by giving devices information about when interrupts
and other activity will have a reduced power impact.  It requires
support from both the device and system (i.e. not only does the device
need to respond to OBFF messages, but the platform must be capable of
generating and routing them to the end point).

Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

1 files changed, 92 insertions, 0 deletions

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index d0182be..01e4cab 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -1887,6 +1887,98 @@ void pci_disable_ido(struct pci_dev *dev, unsigned long type)
 }
 EXPORT_SYMBOL(pci_disable_ido);
 
+/**
+ * pci_enable_obff - enable optimized buffer flush/fill
+ * @dev: PCI device
+ * @type: type of signaling to use
+ *
+ * Try to enable @type OBFF signaling on @dev.  It will try using WAKE#
+ * signaling if possible, falling back to message signaling only if
+ * WAKE# isn't supported.  @type should indicate whether the PCIe link
+ * be brought out of L0s or L1 to send the message.  It should be either
+ * %PCI_EXP_OBFF_SIGNAL_ALWAYS or %PCI_OBFF_SIGNAL_L0.
+ *
+ * If your device can benefit from receiving all messages, even at the
+ * power cost of bringing the link back up from a low power state, use
+ * %PCI_EXP_OBFF_SIGNAL_ALWAYS.  Otherwise, use %PCI_OBFF_SIGNAL_L0 (the
+ * preferred type).
+ *
+ * RETURNS:
+ * Zero on success, appropriate error number on failure.
+ */
+int pci_enable_obff(struct pci_dev *dev, enum pci_obff_signal_type type)
+{
+	int pos;
+	u32 cap;
+	u16 ctrl;
+	int ret;
+
+	if (!pci_is_pcie(dev))
+		return -ENOTSUPP;
+
+	pos = pci_pcie_cap(dev);
+	if (!pos)
+		return -ENOTSUPP;
+
+	pci_read_config_dword(dev, pos + PCI_EXP_DEVCAP2, &cap);
+	if (!(cap & PCI_EXP_OBFF_MASK))
+		return -ENOTSUPP; /* no OBFF support at all */
+
+	/* Make sure the topology supports OBFF as well */
+	if (dev->bus) {
+		ret = pci_enable_obff(dev->bus->self, type);
+		if (ret)
+			return ret;
+	}
+
+	pci_read_config_word(dev, pos + PCI_EXP_DEVCTL2, &ctrl);
+	if (cap & PCI_EXP_OBFF_WAKE)
+		ctrl |= PCI_EXP_OBFF_WAKE_EN;
+	else {
+		switch (type) {
+		case PCI_EXP_OBFF_SIGNAL_L0:
+			if (!(ctrl & PCI_EXP_OBFF_WAKE_EN))
+				ctrl |= PCI_EXP_OBFF_MSGA_EN;
+			break;
+		case PCI_EXP_OBFF_SIGNAL_ALWAYS:
+			ctrl &= ~PCI_EXP_OBFF_WAKE_EN;
+			ctrl |= PCI_EXP_OBFF_MSGB_EN;
+			break;
+		default:
+			WARN(1, "bad OBFF signal type\n");
+			return -ENOTSUPP;
+		}
+	}
+	pci_write_config_word(dev, pos + PCI_EXP_DEVCTL2, ctrl);
+
+	return 0;
+}
+EXPORT_SYMBOL(pci_enable_obff);
+
+/**
+ * pci_disable_obff - disable optimized buffer flush/fill
+ * @dev: PCI device
+ *
+ * Disable OBFF on @dev.
+ */
+void pci_disable_obff(struct pci_dev *dev)
+{
+	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);
+	ctrl &= ~PCI_EXP_OBFF_WAKE_EN;
+	pci_write_config_word(dev, pos + PCI_EXP_DEVCTL2, ctrl);
+}
+EXPORT_SYMBOL(pci_disable_obff);
+
 static int pci_acs_enable;
 
 /**