[PATCH] msi: sanely support hardware level msi disabling

In some cases when we are not using msi we need a way to ensure that the
hardware does not have an msi capability enabled.  Currently the code has been
calling disable_msi_mode to try and achieve that.  However disable_msi_mode
has several other side effects and is only available when msi support is
compiled in so it isn't really appropriate.

Instead this patch implements pci_msi_off which disables all msi and msix
capabilities unconditionally with no additional side effects.

pci_disable_device was redundantly clearing the bus master enable flag and
clearing the msi enable bit.  A device that is not allowed to perform bus
mastering operations cannot generate intx or msi interrupt messages as those
are essentially a special case of dma, and require bus mastering.  So the call
in pci_disable_device to disable msi capabilities was redundant.

quirk_pcie_pxh also called disable_msi_mode and is updated to use pci_msi_off.
Signed-off-by: NEric W. Biederman <ebiederm@xmission.com>
Cc: Michael Ellerman <michael@ellerman.id.au>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Greg KH <greg@kroah.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

arch/powerpc/kernel/irq.c

@@ -968,7 +968,6 @@ void pci_scan_msi_device(struct pci_dev *dev) {}
 int pci_enable_msix(struct pci_dev* dev, struct msix_entry *entries, int nvec) {return -1;}
 void pci_disable_msix(struct pci_dev *dev) {}
 void msi_remove_pci_irq_vectors(struct pci_dev *dev) {}
-void disable_msi_mode(struct pci_dev *dev, int pos, int type) {}
 void pci_no_msi(void) {}
 EXPORT_SYMBOL(pci_enable_msix);
 EXPORT_SYMBOL(pci_disable_msix);

drivers/pci/msi.c

@@ -211,7 +211,7 @@ static void enable_msi_mode(struct pci_dev *dev, int pos, int type)
 	pci_intx(dev, 0);  /* disable intx */
 }
 
-void disable_msi_mode(struct pci_dev *dev, int pos, int type)
+static void disable_msi_mode(struct pci_dev *dev, int pos, int type)
 {
 	u16 control;
 

drivers/pci/pci.c

@@ -881,13 +881,6 @@ pci_disable_device(struct pci_dev *dev)
 	if (atomic_sub_return(1, &dev->enable_cnt) != 0)
 		return;
 
-	if (dev->msi_enabled)
-		disable_msi_mode(dev, pci_find_capability(dev, PCI_CAP_ID_MSI),
-			PCI_CAP_ID_MSI);
-	if (dev->msix_enabled)
-		disable_msi_mode(dev, pci_find_capability(dev, PCI_CAP_ID_MSI),
-			PCI_CAP_ID_MSIX);
-
 	pci_read_config_word(dev, PCI_COMMAND, &pci_command);
 	if (pci_command & PCI_COMMAND_MASTER) {
 		pci_command &= ~PCI_COMMAND_MASTER;
@@ -1277,6 +1270,33 @@ pci_intx(struct pci_dev *pdev, int enable)
 	}
 }
 
+/**
+ * pci_msi_off - disables any msi or msix capabilities
+ * @pdev: the PCI device to operate on
+ *
+ * If you want to use msi see pci_enable_msi and friends.
+ * This is a lower level primitive that allows us to disable
+ * msi operation at the device level.
+ */
+void pci_msi_off(struct pci_dev *dev)
+{
+	int pos;
+	u16 control;
+
+	pos = pci_find_capability(dev, PCI_CAP_ID_MSI);
+	if (pos) {
+		pci_read_config_word(dev, pos + PCI_MSI_FLAGS, &control);
+		control &= ~PCI_MSI_FLAGS_ENABLE;
+		pci_write_config_word(dev, pos + PCI_MSI_FLAGS, 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;
+		pci_write_config_word(dev, pos + PCI_MSIX_FLAGS, control);
+	}
+}
+
 #ifndef HAVE_ARCH_PCI_SET_DMA_MASK
 /*
  * These can be overridden by arch-specific implementations

drivers/pci/pci.h

@@ -46,10 +46,8 @@ extern struct rw_semaphore pci_bus_sem;
 extern unsigned int pci_pm_d3_delay;
 
 #ifdef CONFIG_PCI_MSI
-void disable_msi_mode(struct pci_dev *dev, int pos, int type);
 void pci_no_msi(void);
 #else
-static inline void disable_msi_mode(struct pci_dev *dev, int pos, int type) { }
 static inline void pci_no_msi(void) { }
 #endif
 

drivers/pci/quirks.c

@@ -1438,8 +1438,8 @@ DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_INTEL,	PCI_DEVICE_ID_INTEL_E7525_MCH,	quir
  */
 static void __devinit quirk_pcie_pxh(struct pci_dev *dev)
 {
-	disable_msi_mode(dev, pci_find_capability(dev, PCI_CAP_ID_MSI),
-					PCI_CAP_ID_MSI);
+	pci_msi_off(dev);
+
 	dev->no_msi = 1;
 
 	printk(KERN_WARNING "PCI: PXH quirk detected, "

include/linux/pci.h

@@ -543,6 +543,7 @@ void pci_set_master(struct pci_dev *dev);
 int __must_check pci_set_mwi(struct pci_dev *dev);
 void pci_clear_mwi(struct pci_dev *dev);
 void pci_intx(struct pci_dev *dev, int enable);
+void pci_msi_off(struct pci_dev *dev);
 int pci_set_dma_mask(struct pci_dev *dev, u64 mask);
 int pci_set_consistent_dma_mask(struct pci_dev *dev, u64 mask);
 void pci_update_resource(struct pci_dev *dev, struct resource *res, int resno);

include/linux/pci_regs.h

@@ -292,7 +292,8 @@
 #define PCI_MSI_DATA_64		12	/* 16 bits of data for 64-bit devices */
 #define PCI_MSI_MASK_BIT	16	/* Mask bits register */
 
-/* MSI-X registers (these are at offset PCI_MSI_FLAGS) */
+/* MSI-X registers (these are at offset PCI_MSIX_FLAGS) */
+#define PCI_MSIX_FLAGS		2
 #define  PCI_MSIX_FLAGS_QSIZE	0x7FF
 #define  PCI_MSIX_FLAGS_ENABLE	(1 << 15)
 #define PCI_MSIX_FLAGS_BIRMASK	(7 << 0)