PCI: Cache MSI/MSI-X capability offsets in struct pci_dev

The patch caches the MSI and MSI-X capability offset in PCI device
(struct pci_dev) so that we needn't read it from the config space
upon enabling or disabling MSI or MSI-X interrupts.

[bhelgaas: moved pm_cap size change to separate patch]
Signed-off-by: NGavin Shan <shangw@linux.vnet.ibm.com>
Signed-off-by: NBjorn Helgaas <bhelgaas@google.com>

drivers/pci/msi.c

@@ -111,32 +111,26 @@ void default_restore_msi_irqs(struct pci_dev *dev, int irq)
 }
 #endif
 
-static void msi_set_enable(struct pci_dev *dev, int pos, int enable)
+static void msi_set_enable(struct pci_dev *dev, int enable)
 {
 	u16 control;
 
-	BUG_ON(!pos);
-
-	pci_read_config_word(dev, pos + PCI_MSI_FLAGS, &control);
+	pci_read_config_word(dev, dev->msi_cap + PCI_MSI_FLAGS, &control);
 	control &= ~PCI_MSI_FLAGS_ENABLE;
 	if (enable)
 		control |= PCI_MSI_FLAGS_ENABLE;
-	pci_write_config_word(dev, pos + PCI_MSI_FLAGS, control);
+	pci_write_config_word(dev, dev->msi_cap + PCI_MSI_FLAGS, control);
 }
 
 static void msix_set_enable(struct pci_dev *dev, int enable)
 {
-	int pos;
 	u16 control;
 
-	pos = pci_find_capability(dev, PCI_CAP_ID_MSIX);
-	if (pos) {
-		pci_read_config_word(dev, pos + PCI_MSIX_FLAGS, &control);
-		control &= ~PCI_MSIX_FLAGS_ENABLE;
-		if (enable)
-			control |= PCI_MSIX_FLAGS_ENABLE;
-		pci_write_config_word(dev, pos + PCI_MSIX_FLAGS, control);
-	}
+	pci_read_config_word(dev, dev->msix_cap + PCI_MSIX_FLAGS, &control);
+	control &= ~PCI_MSIX_FLAGS_ENABLE;
+	if (enable)
+		control |= PCI_MSIX_FLAGS_ENABLE;
+	pci_write_config_word(dev, dev->msix_cap + PCI_MSIX_FLAGS, control);
 }
 
 static inline __attribute_const__ u32 msi_mask(unsigned x)
@@ -402,7 +396,7 @@ static void __pci_restore_msi_state(struct pci_dev *dev)
 	pos = entry->msi_attrib.pos;
 
 	pci_intx_for_msi(dev, 0);
-	msi_set_enable(dev, pos, 0);
+	msi_set_enable(dev, 0);
 	arch_restore_msi_irqs(dev, dev->irq);
 
 	pci_read_config_word(dev, pos + PCI_MSI_FLAGS, &control);
@@ -557,7 +551,7 @@ static int msi_capability_init(struct pci_dev *dev, int nvec)
 	unsigned mask;
 
 	pos = pci_find_capability(dev, PCI_CAP_ID_MSI);
-	msi_set_enable(dev, pos, 0);	/* Disable MSI during set up */
+	msi_set_enable(dev, 0);	/* Disable MSI during set up */
 
 	pci_read_config_word(dev, msi_control_reg(pos), &control);
 	/* MSI Entry Initialization */
@@ -598,7 +592,7 @@ static int msi_capability_init(struct pci_dev *dev, int nvec)
 
 	/* Set MSI enabled bits	 */
 	pci_intx_for_msi(dev, 0);
-	msi_set_enable(dev, pos, 1);
+	msi_set_enable(dev, 1);
 	dev->msi_enabled = 1;
 
 	dev->irq = entry->irq;
@@ -885,7 +879,7 @@ void pci_msi_shutdown(struct pci_dev *dev)
 	desc = list_first_entry(&dev->msi_list, struct msi_desc, list);
 	pos = desc->msi_attrib.pos;
 
-	msi_set_enable(dev, pos, 0);
+	msi_set_enable(dev, 0);
 	pci_intx_for_msi(dev, 1);
 	dev->msi_enabled = 0;
 
@@ -1048,15 +1042,17 @@ EXPORT_SYMBOL(pci_msi_enabled);
 
 void pci_msi_init_pci_dev(struct pci_dev *dev)
 {
-	int pos;
 	INIT_LIST_HEAD(&dev->msi_list);
 
 	/* Disable the msi hardware to avoid screaming interrupts
 	 * during boot.  This is the power on reset default so
 	 * usually this should be a noop.
 	 */
-	pos = pci_find_capability(dev, PCI_CAP_ID_MSI);
-	if (pos)
-		msi_set_enable(dev, pos, 0);
-	msix_set_enable(dev, 0);
+	dev->msi_cap = pci_find_capability(dev, PCI_CAP_ID_MSI);
+	if (dev->msi_cap)
+		msi_set_enable(dev, 0);
+
+	dev->msix_cap = pci_find_capability(dev, PCI_CAP_ID_MSIX);
+	if (dev->msix_cap)
+		msix_set_enable(dev, 0);
 }

include/linux/pci.h

@@ -232,6 +232,8 @@ struct pci_dev {
 	u8		revision;	/* PCI revision, low byte of class word */
 	u8		hdr_type;	/* PCI header type (`multi' flag masked out) */
 	u8		pcie_cap;	/* PCI-E capability offset */
+	u8		msi_cap;	/* MSI capability offset */
+	u8		msix_cap;	/* MSI-X capability offset */
 	u8		pcie_mpss:3;	/* PCI-E Max Payload Size Supported */
 	u8		rom_base_reg;	/* which config register controls the ROM */
 	u8		pin;  		/* which interrupt pin this device uses */